Wiki links starting with / are always relative to the wiki root

Also, links with the file: scheme are absolute iff they start with / or
drive letter

Ref #105

autoload/vimwiki/path.vim

@@ -49,10 +49,7 @@ endfunction "}}}
 function! vimwiki#path#is_link_to_dir(link) "{{{
   " Check if link is to a directory.
   " It should be ended with \ or /.
-  if a:link =~# '.\+[/\\]$'
-    return 1
-  endif
-  return 0
+  return a:link =~# '\m[/\\]$'
 endfunction "}}}
 
 function! vimwiki#path#abs_path_of_link(link) "{{{