add slim-lint (#388)

* add slim-lint

* add slim readme entry

* add slim entry to doc

* add slimlint vader test

ale_linters/slim/slimlint.vim

@@ -0,0 +1,33 @@
+" Author: Markus Doits - https://github.com/doits
+" Description: slim-lint for Slim files, based on hamllint.vim
+
+function! ale_linters#slim#slimlint#Handle(buffer, lines) abort
+    " Matches patterns like the following:
+    " <path>:5 [W] LineLength: Line is too long. [150/120]
+    let l:pattern = '\v^.*:(\d+) \[([EW])\] (.+)$'
+    let l:output = []
+
+    for l:line in a:lines
+        let l:match = matchlist(l:line, l:pattern)
+
+        if len(l:match) == 0
+            continue
+        endif
+
+        call add(l:output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': l:match[1] + 0,
+        \   'type': l:match[2],
+        \   'text': l:match[3]
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('slim', {
+\   'name': 'slimlint',
+\   'executable': 'slim-lint',
+\   'command': 'slim-lint %t',
+\   'callback': 'ale_linters#slim#slimlint#Handle'
+\})