Add g:tagbar_scopestrs (#661)

Allows mapping scope suffixes (e.g. 'function') to user-defined values.

plugin/tagbar.vim

@@ -95,6 +95,7 @@ function! s:setup_options() abort
         \ ['hide_nonpublic', 0],
         \ ['height', 10],
         \ ['indent', 2],
+        \ ['scopestrs', {}],
         \ ['left', 0],
         \ ['position', default_pos],
         \ ['previewwin_pos', previewwin_pos],