Add NeoVim compatibility

Author: alerque

plugin/criticmarkup.vim

@@ -2,4 +2,14 @@ augroup criticmarkup
     autocmd!
     autocmd Filetype pandoc,markdown,mkd,txt call criticmarkup#Init()
     autocmd Syntax pandoc,markdown,mkd,txt call criticmarkup#InjectHighlighting()
+    " The unorthodox way this plugin injects new syntax rules is broken in
+    " Neovim which takes a different approach to initializing the GUI (which
+    " is an optional component rather than an assumed part of the system). As
+    " a result we don't get initialized at all unless the user happens to
+    " set filetype a second time after initial loading or loads a buffer after
+    " the GUI is loaded. This hack sidesteps that and makes sure we get a
+    " chance to get started. See https://github.com/neovim/neovim/issues/2953
+    if has('nvim')
+        autocmd VimEnter * doautoa Syntax,Filetype
+    endif
 augroup END