Using arange within a [] expression fails
The following code fails:

```nim
let numItems = 3
let start = 2
let v = @[10, 11, 12, 13, 14, 15].toTensor
let w = v[start +. arange(numItems)]
echo w
```
with the following error:

```
C:\Arraymancer\my_test.nim(50, 10) template/generic instantiation of `[]` from here
C:\Arraymancer\src\arraymancer\tensor\accessors_macros_read.nim(55, 12) template/generic instantiation of `slice_typed_dispatch` from here
C:\Arraymancer\src\arraymancer\tensor\init_cpu.nim(199, 23) Error: expression 'T(1)' has no type (or is ambiguous)
```
I will send a PR to fix this soon.
