Support TagBar for snippets files

Bundle an exuberant ctags definition for UltiSnips and tell TagBar how
to find it.

ctags/UltiSnips.cnf

@@ -0,0 +1,3 @@
+--langdef=UltiSnips
+--langmap=UltiSnips:.snippets
+--regex-UltiSnips=/^snippet (.*)/\1/s,snippet/

ftplugin/snippets.vim

@@ -15,3 +15,12 @@ if exists("loaded_matchit") && !exists("b:match_words")
   let b:match_ignorecase = 0
   let b:match_words = '^snippet\>:^endsnippet\>,^global\>:^endglobal\>,\${:}'
 endif
+
+" Add TagBar support
+let g:tagbar_type_snippets = {
+            \ 'ctagstype': 'UltiSnips',
+            \ 'kinds': [
+                \ 's:snippets',
+            \ ],
+            \ 'deffile': expand('<sfile>:p:h:h') . '/ctags/UltiSnips.cnf',
+        \ }