Improvement for Syntax guide

While translating the page I did a couple of changes to XWikiSyntax.xml. Most of them are just typos, dupe information or inconsistencies in the wording.

I put quite a lot of work into the link specifications and they should be more precise and more complete now.

Attached to this issue you will find the appropriate patch created I created with the help of Caleb who contributed the fix for the Firefox weirdness.