Unable to install with Ubuntu version of nim
Trying to install inim with nim 1.0.6 ([provided by Ubuntu 20.04.2 LTS](https://packages.ubuntu.com/focal/nim)), I get the following error: `Error: undeclared field: 'isEmptyOrWhitespace' for type system.string [declared in /usr/lib/nim/system.nim(49, 3)]`.

Maybe a minimum language version should be added to https://github.com/inim-repl/INim/blob/53a18a52f6a427ea273182ebb658ad2a28a7d333/inim.nimble#L12-L16

The offending line is https://github.com/inim-repl/INim/blob/53a18a52f6a427ea273182ebb658ad2a28a7d333/inim.nim#L207

## Version info, etc.

The following is what is provided by `apt` in Ubuntu:

```bash
$ nim --version
Nim Compiler Version 1.0.6 [Linux: amd64]
Compiled at 2020-02-27
Copyright (c) 2006-2019 by Andreas Rumpf

active boot switches: -d:release

$ nimble --version
nimble v0.11.0 compiled at 2020-02-27 15:07:29
git hash: couldn't determine git hash

```

## Full output

```bash
$ nimble install inim --verbose
    Reading official package list
Downloading https://github.com/inim-repl/INim using git
    Cloning latest tagged version: v0.6.1
  Verifying dependencies for inim@0.6.1
    Reading official package list
   Checking for cligen@>= 1.2.0
      Info: Dependency on cligen@>= 1.2.0 already satisfied
  Verifying dependencies for cligen@1.5.4
    Reading official package list
   Checking for noise@>= 0.1.4
      Info: Dependency on noise@>= 0.1.4 already satisfied
  Verifying dependencies for noise@0.1.4
 Installing inim@0.6.1
   Building inim/inim using c backend
    Prompt: Build failed for 'inim@0.6.1', would you like to try installing 'inim@#head' (latest unstable)? [y/N]
    Answer: y
    Reading official package list
Downloading https://github.com/inim-repl/INim using git
   Warning: Package 'inim' has an incorrect structure. It should contain a single directory hierarchy for source files, named 'inimpkg', but file 'test_piping_with_end_echo.nim' is in a directory named 'tests' instead. This will be an error in the future.
      Hint: If 'tests' contains source files for building 'inim', rename it to 'inimpkg'. Otherwise, prevent its installation by adding `skipDirs = @["tests"]` to the .nimble file.
  Verifying dependencies for inim@#head
    Reading official package list
   Checking for cligen@>= 1.2.0
      Info: Dependency on cligen@>= 1.2.0 already satisfied
  Verifying dependencies for cligen@1.5.4
    Reading official package list
   Checking for noise@>= 0.1.4
      Info: Dependency on noise@>= 0.1.4 already satisfied
  Verifying dependencies for noise@0.1.4
 Installing inim@#head
   Building inim/inim using c backend
     Error: Build failed for package: inim
        ... Details:
        ... Execution failed with exit code 1
        ... Command: "/usr/bin/nim" c --noNimblePath -d:NimblePkgVersion=0.6.1 -d:release --path:"/home/schneider/.nimble/pkgs/cligen-1.5.4"  --path:"/home/schneider/.nimble/pkgs/noise-0.1.4"  -o:"/tmp/nimble_18336/githubcom_inimreplINim_#head/inim" "/tmp/nimble_18336/githubcom_inimreplINim_#head/inim.nim"
        ... Output: Hint: used config file '/etc/nim/nim.cfg' [Conf]
        ... Hint: system [Processing]
        ... Hint: widestrs [Processing]
        ... Hint: io [Processing]
        ... Hint: inim [Processing]
        ... Hint: os [Processing]
        ... Hint: strutils [Processing]
        ... Hint: parseutils [Processing]
        ... Hint: math [Processing]
        ... Hint: bitops [Processing]
        ... Hint: macros [Processing]
        ... Hint: algorithm [Processing]
        ... Hint: unicode [Processing]
        ... Hint: pathnorm [Processing]
        ... Hint: osseps [Processing]
        ... Hint: posix [Processing]
        ... Hint: times [Processing]
        ... Hint: options [Processing]
        ... Hint: typetraits [Processing]
        ... Hint: osproc [Processing]
        ... Hint: strtabs [Processing]
        ... Hint: hashes [Processing]
        ... Hint: streams [Processing]
        ... Hint: cpuinfo [Processing]
        ... Hint: linux [Processing]
        ... Hint: strformat [Processing]
        ... Hint: terminal [Processing]
        ... Hint: colors [Processing]
        ... Hint: termios [Processing]
        ... Hint: sequtils [Processing]
        ... Hint: parsecfg [Processing]
        ... Hint: lexbase [Processing]
        ... Hint: tables [Processing]
        ... Hint: sugar [Processing]
        ... Hint: noise [Processing]
        ... Hint: basic [Processing]
        ... Hint: wtf8 [Processing]
        ... Hint: wcwidth [Processing]
        ... Hint: styler [Processing]
        ... Hint: posixio [Processing]
        ... Hint: prompt [Processing]
        ... Hint: history [Processing]
        ... Hint: killring [Processing]
        ... Hint: deques [Processing]
        ... /tmp/nimble_18336/githubcom_inimreplINim_#head/inim.nim(207, 52) Error: undeclared field: 'isEmptyOrWhitespace' for type system.string [declared in /usr/lib/nim/system.nim(49, 3)]
```