Removed syntastic and replaced it with ale

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

sources_non_forked/ale/ale_linters/markdown/markdownlint.vim

@@ -0,0 +1,11 @@
+" Author: Ty-Lucas Kelley <tylucaskelley@gmail.com>
+" Description: Adds support for markdownlint
+
+call ale#linter#Define('markdown', {
+    \ 'name': 'markdownlint',
+    \ 'executable': 'markdownlint',
+    \ 'lint_file': 1,
+    \ 'output_stream': 'both',
+    \ 'command': 'markdownlint %s',
+    \ 'callback': 'ale#handlers#markdownlint#Handle'
+\ })