Add preliminary tagbar support

ftplugin/elm/tagbar.vim

@@ -0,0 +1,20 @@
+if !executable('ctags')
+    finish
+elseif globpath(&rtp, 'plugin/tagbar.vim') == ""
+    finish
+endif
+
+function! s:SetTagbar()
+    if !exists("g:tagbar_type_elm")
+        let g:tagbar_type_elm = {
+                    \ 'ctagstype' : 'elm',
+                    \ 'kinds'     : [
+                    \ 'c:contants',
+                    \ 'f:functions',
+                    \ 'p:ports'
+                    \ ]
+                    \ }
+    endif
+endfunction
+
+call s:SetTagbar()