Removed syntastic and replaced it with ale

Read more here:
https://github.com/w0rp/ale

sources_non_forked/ale/ale_linters/slim/slimlint.vim

@@ -0,0 +1,55 @@
+" Author: Markus Doits - https://github.com/doits
+" Description: slim-lint for Slim files
+
+function! ale_linters#slim#slimlint#GetCommand(buffer) abort
+    let l:command = 'slim-lint %t'
+
+    let l:rubocop_config = ale#path#FindNearestFile(a:buffer, '.rubocop.yml')
+
+    " Set SLIM_LINT_RUBOCOP_CONF variable as it is needed for slim-lint to
+    " pick up the rubocop config.
+    "
+    " See https://github.com/sds/slim-lint/blob/master/lib/slim_lint/linter/README.md#rubocop
+    if !empty(l:rubocop_config)
+      if ale#Has('win32')
+        let l:command = 'set SLIM_LINT_RUBOCOP_CONF=' . ale#Escape(l:rubocop_config) . ' && ' . l:command
+      else
+        let l:command = 'SLIM_LINT_RUBOCOP_CONF=' . ale#Escape(l:rubocop_config) . ' ' . l:command
+      endif
+    endif
+
+    return l:command
+endfunction
+
+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+) \[([EW])\] (.+)$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        let l:item = {
+        \   'lnum': l:match[1] + 0,
+        \   'type': l:match[2],
+        \   'text': l:match[3]
+        \}
+
+        let l:code_match = matchlist(l:item.text, '\v^([^:]+): (.+)$')
+
+        if !empty(l:code_match)
+            let l:item.code = l:code_match[1]
+            let l:item.text = l:code_match[2]
+        endif
+
+        call add(l:output, l:item)
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('slim', {
+\   'name': 'slimlint',
+\   'executable': 'slim-lint',
+\   'command_callback': 'ale_linters#slim#slimlint#GetCommand',
+\   'callback': 'ale_linters#slim#slimlint#Handle'
+\})