add textlint support for markdown (#1383)

autoload/ale/handlers/textlint.vim

@@ -0,0 +1,19 @@
+" Author: tokida https://rouger.info
+" Description: Redpen, a proofreading tool (http://redpen.cc)
+
+function! ale#handlers#textlint#HandleTextlintOutput(buffer, lines) abort
+    let l:res = get(ale#util#FuzzyJSONDecode(a:lines, []), 0, {'messages': []})
+    let l:output = []
+
+    for l:err in l:res.messages
+        call add(l:output, {
+        \   'text': l:err.message,
+        \   'type': 'W',
+        \   'code': l:err.ruleId,
+        \   'lnum': l:err.line,
+        \   'col' : l:err.column
+        \})
+    endfor
+
+    return l:output
+endfunction