Add linter for Inko

This adds a linter for Inko (https://inko-lang.org/). The linter makes
use of Inko's own compiler, and a newly introduced --check flag to only
check for errors; instead of also compiling source code.

doc/ale-inko.txt

@@ -0,0 +1,22 @@
+===============================================================================
+ALE Inko Integration                                         *ale-inko-options*
+                                                         *ale-integration-inko*
+
+===============================================================================
+Integration Information
+
+  Currently, the only supported linter for Inko is the Inko compiler itself.
+
+===============================================================================
+inko                                                            *ale-inko-inko*
+
+g:ale_inko_inko_executable                         *g:ale_inko_inko_executable*
+                                                   *b:ale_inko_inko_executable*
+  Type: |String|
+  Default: `'inko'`
+
+  This variable can be modified to change the executable path for `inko`.
+
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale-supported-languages-and-tools.txt

@@ -213,6 +213,8 @@ Notes:
   * `idris`
 * Ink
   * `ink-language-server`
+* Inko
+  * `inko` !!
 * ISPC
   * `ispc`!!
 * Java

doc/ale.txt

@@ -1502,6 +1502,7 @@ g:ale_linters                                                   *g:ale_linters*
   \   'go': ['gofmt', 'golint', 'go vet'],
   \   'hack': ['hack'],
   \   'help': [],
+  \   'inko': ['inko'],
   \   'perl': ['perlcritic'],
   \   'perl6': [],
   \   'python': ['flake8', 'mypy', 'pylint', 'pyright'],
@@ -2656,6 +2657,8 @@ documented in additional help files.
     idris.................................|ale-idris-idris|
   ink.....................................|ale-ink-options|
     ink-language-server...................|ale-ink-language-server|
+  inko....................................|ale-inko-options|
+    inko..................................|ale-inko-inko|
   ispc....................................|ale-ispc-options|
     ispc..................................|ale-ispc-ispc|
   java....................................|ale-java-options|