Feature Request: Ignore anonymous option (#727)

Closes #726

New option `g:tagbar_ignore_anonymous` to ignore any tags with __anon in
the tag name. CTAGS will print any unlabeled tags with the __anon###
name with a custom hash. This option will ignore those tags and they
will not be visible in the tagbar window. This could potentially result
in unknown behavior when a parent object has been ignored in this way.
However these tags should then fall under the default hierarchy for that
particular kind.

autoload/tagbar.vim

@@ -1281,6 +1281,11 @@ function! s:ProcessFile(fname, ftype) abort
         if line =~# '^!_TAG_' || has_key(seen, line)
             continue
         endif
+        if g:tagbar_ignore_anonymous && line =~# '__anon'
+            call tagbar#debug#log('anonymous tag found - ignoring per tagbar configuration')
+            continue
+        endif
+
         let seen[line] = 1
 
         let parts = split(line, ';"')