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.

doc/tagbar.txt

@@ -1140,6 +1140,17 @@ highlight the 'SOME_MACRO' tag.
 Example: >
         let g:tagbar_highlight_method = 'nearest'
 <
+                                                    *g:tagbar_ignore_anonymous*
+g:tagbar_ignore_anonymous~
+Default: 0
+
+If set, any '__anon' tags generated by ctags will be ignored and will not be
+displayed in the tagbar window. Note: this will also mean any child tags of
+that anonymous tag will also not be visible.
+
+Example: >
+    let g:tagbar_ignore_anonymous = 1
+<
 
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 HIGHLIGHT COLOURS                                           *tagbar-highlight*