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

test/link_markdown_multiple_per_file.vader

@@ -2,18 +2,18 @@ Include: vader_includes/vader_setup.vader
 
 Given vimwiki (Internal links + one link to filenew):
   # Contents
-  
+
     - [Test1](#Test1)
     - [Test2](#Test2)
-  
+
   # Test1
-  
+
     - [Test1](#Test1)
     - [Test2](#Test2)
     - [filenew](filenew)
-  
+
   # Test2
-  
+
     - [Test1](#Test1)
     - [Test2](#Test2)
     - [filenew](filenew)