Deprecation warning when using `map`
I've found when using the `map` function (among others) I get a compile-time warning. Here is a reproducer:
```nim
import arraymancer
import sugar

func expPlus1*[T: SomeNumber](x: Tensor[T]): Tensor[T] =
  x.map(y => exp(y + 1))

let a = [-2.0, -1.0, 0.0, 1.0, 2.0].toTensor()
echo expPlus1(a)
```
This gives compile-time warnings

```
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `expPlus1` from here
/home/chris/Code/minexample.nim(5, 4) template/generic instantiation of `map` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/higher_order_applymap.nim(137, 9) template/generic instantiation of `apply2_inline` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/higher_order_applymap.nim(36, 43) template/generic instantiation of `mzip` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/accessors.nim(188, 27) template/generic instantiation of `check_contiguous_index` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_checks.nim(38, 24) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `$` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/display.nim(27, 27) template/generic instantiation of `disp3d` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_display.nim(93, 14) template/generic instantiation of `axis` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/accessors.nim(311, 15) template/generic instantiation of `axisIterator` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/accessors.nim(277, 21) template/generic instantiation of `check_axis_index` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_checks.nim(143, 24) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `$` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/display.nim(27, 27) template/generic instantiation of `disp3d` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_display.nim(95, 49) template/generic instantiation of `reshape` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/shapeshifting.nim(70, 14) template/generic instantiation of `reshapeImpl` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_shapeshifting.nim(55, 22) template/generic instantiation of `reshape_with_copy` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_shapeshifting.nim(34, 9) template/generic instantiation of `apply2_inline` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/higher_order_applymap.nim(36, 43) template/generic instantiation of `mzip` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/accessors.nim(188, 27) template/generic instantiation of `check_contiguous_index` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_checks.nim(38, 24) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `$` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/display.nim(27, 27) template/generic instantiation of `disp3d` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_display.nim(96, 32) template/generic instantiation of `[]` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/accessors_macros_read.nim(55, 12) template/generic instantiation of `slice_typed_dispatch` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors.nim(81, 20) template/generic instantiation of `getIndex` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors.nim(63, 6) template/generic instantiation of `check_index` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_checks.nim(31, 24) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `$` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/display.nim(27, 27) template/generic instantiation of `disp3d` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_display.nim(94, 20) template/generic instantiation of `concat` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/shapeshifting.nim(225, 11) template/generic instantiation of `slicerMut` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_write.nim(149, 18) template/generic instantiation of `slicerMutImpl_T` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_write.nim(139, 17) template/generic instantiation of `slicer` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_read.nim(65, 13) template/generic instantiation of `slicerImpl` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_read.nim(31, 25) template/generic instantiation of `newException` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_read.nim(32, 9) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `$` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/display.nim(27, 27) template/generic instantiation of `disp3d` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_display.nim(94, 20) template/generic instantiation of `concat` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/shapeshifting.nim(225, 11) template/generic instantiation of `slicerMut` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_write.nim(149, 18) template/generic instantiation of `slicerMutImpl_T` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors_macros_write.nim(142, 16) template/generic instantiation of `check_shape` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_checks.nim(90, 24) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
/home/chris/Code/minexample.nim(8, 14) template/generic instantiation of `$` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/display.nim(29, 27) template/generic instantiation of `disp4d` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_display.nim(131, 30) template/generic instantiation of `[]` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/accessors_macros_read.nim(55, 12) template/generic instantiation of `slice_typed_dispatch` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors.nim(81, 20) template/generic instantiation of `getIndex` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_accessors.nim(63, 6) template/generic instantiation of `check_index` from here
/home/chris/.nimble/pkgs/arraymancer-0.6.1/arraymancer/tensor/private/p_checks.nim(31, 24) Warning: See corresponding Defect; IndexError is deprecated [Deprecated]
```
It appears that a deprecated feature is being used in the back-end.