Removed syntastic and replaced it with ale

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

sources_non_forked/ale/ale_linters/markdown/textlint.vim

@@ -0,0 +1,9 @@
+" Author: tokida https://rouger.info, Yasuhiro Kiyota <yasuhiroki.duck@gmail.com>
+" Description: textlint, a proofreading tool (https://textlint.github.io/)
+
+call ale#linter#Define('markdown', {
+\   'name': 'textlint',
+\   'executable_callback': 'ale#handlers#textlint#GetExecutable',
+\   'command_callback': 'ale#handlers#textlint#GetCommand',
+\   'callback': 'ale#handlers#textlint#HandleTextlintOutput',
+\})