Add Ruby MRI linter (#453)

* Added ruby mri linter

* Added to the list of supported linters

* Async and now with 4 spaces

* Vader tests for ruby

* Match style choices

* Vader test for the Ruby handler now works and passes

ale_linters/ruby/ruby.vim

@@ -0,0 +1,40 @@
+" Author: Brandon Roehl - https://github.com/BrandonRoehl
+" Description: Ruby MRI for Ruby files
+
+function! ale_linters#ruby#ruby#Handle(buffer, lines) abort
+    " Matches patterns line the following:
+    "
+    " test.rb:3: warning: parentheses after method name is interpreted as an argument list, not a decomposed argument
+    " test.rb:8: syntax error, unexpected keyword_end, expecting end-of-input
+    let l:pattern = '\v^.+:(\d+): (warning: )?(.+)$'
+    let l:column = '\v^(\s+)\^$'
+    let l:output = []
+
+    for l:line in a:lines
+        let l:match = matchlist(l:line, l:pattern)
+        if len(l:match) == 0
+            let l:match = matchlist(l:line, l:column)
+            if len(l:match) != 0
+                let l:output[len(l:output) - 1]['col'] = len(l:match[1])
+            endif
+        else
+            call add(l:output, {
+            \   'bufnr': a:buffer,
+            \   'lnum': l:match[1] + 0,
+            \   'col': 0,
+            \   'text': l:match[2] . l:match[3],
+            \   'type': empty(l:match[2]) ? 'E' : 'W',
+            \})
+        endif
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('ruby', {
+\   'name': 'ruby',
+\   'executable': 'ruby',
+\   'output_stream': 'stderr',
+\   'command': 'ruby -w -c -T1 %t',
+\   'callback': 'ale_linters#ruby#ruby#Handle',
+\})