Refractor: Path Add utility unixify #478

Basically unixify all before workingm then transofom in function os os

Util: Add function sort_len that a list of string according to the lenght of its content
Fix: VimwikiRenameLink doesn't update links in diary #90
Test: VimwikiRenameLink with nested directories
Prettify comments in autoload/path + remove antipattern
Define osxify function helper to solve windows Vs Unix : see #478
Path: remove useless temporary fix convertion before calling relpath (redundant) : see #478
Test: Fix typo
Path corrected (Thanks to test)

autoload/vimwiki/u.vim

@@ -62,6 +62,16 @@ endfunction
 
 
 " Trim spaces: leading and trailing
+function! vimwiki#u#sort_len(list) abort
+  function! s:len_compare(s1, s2) abort
+    let i1 = len(a:s1)
+    let i2 = len(a:s2)
+     return i1 == i2 ? 0 : i1 > i2 ? 1 : -1
+  endfunction
+  return sort(a:list, 's:len_compare')
+endfunction
+
+
 function! vimwiki#u#trim(string, ...) abort
   let chars = ''
   if a:0 > 0