Fix relative paths for VimwikiRenameLink. Merge PR #787.

Fixes #90 

__Problem__: VimwikiRenameLink does not rename dir1/toto url in dir2/tata
because the dirs (dir2 and .) were well crossed but badly inspected.
__Solution__: `blob(.ext*)` -> `glob(**/*.ext)` + find the relative URL

* Fasten: VimwikiRenameLink goes faster with cache
More: To compute old_url regex, use a cache dict because it is the same
for files in the same directories

* Util DeleteHiddenBuffer -> do not delete Vader buffer

* Test: Prettify: Util: teardown delete defined function

* Remove unnecessary trailing spaces
Note: list_VimwikiReturn.vader has some necessary trailing spaces

syntax/vimwiki_markdown_custom.vim

@@ -172,7 +172,7 @@ endif
 
 
 " Tables
-syntax match VimwikiTableRow /^\s*|.\+|\s*$/ 
+syntax match VimwikiTableRow /^\s*|.\+|\s*$/
       \ transparent contains=VimwikiCellSeparator,
                            \ VimwikiLinkT,
                            \ VimwikiWeblink1T,