Add option to set a character which replaces spaces when creating links.

The wikilocal option links_space_char will be used to replace any spaces
when creating a new wiki link and page. This only affects link creation
with a visual selection.

autoload/vimwiki/base.vim

@@ -2134,7 +2134,8 @@ function! s:normalize_link_syntax_v()
     endif
 
     " Put substitution in register " and change text
-    call setreg('"', substitute(sub, '\n', '', ''), visualmode())
+    let sc = vimwiki#vars#get_wikilocal('links_space_char')
+    call setreg('"', substitute(substitute(sub, '\n', '', ''), '\s', sc, 'g'), visualmode())
     normal! `>""pgvd
   finally
     call setreg('"', default_register_save, registertype_save)