Add toc_link_format option

Add an option for setting the format of the links in the Table of Contents:
- Extended (the current and default)
- Brief (new format for the Vimwiki markup)

doc/vimwiki.txt

@@ -2992,6 +2992,21 @@ are from 1 to 6.
 The default is 1.
 
 
+------------------------------------------------------------------------------
+*g:vimwiki_toc_link_format*
+
+The format of the links in the Table of Contents (see |vimwiki-toc|).
+
+
+Value           Description~
+0               Extended: The link contains the description and URL. URL
+                references all levels.
+1               Brief: The link contains only the URL. URL references only
+                the immediate level.
+
+Default: 0
+
+
 ------------------------------------------------------------------------------
 *g:vimwiki_map_prefix*