Favicon support

Hi,

I have added support for adding a user-specifier web page icon to the generated XHTML. 

I had originally patched the big elyxer that is packaged, now I have made an account on Github, forked, split my patch and here it is. If you have a test suite, it is probably a good idea to run it and see no problems are detected. The patch is small anyhow and I have been testing its un-split version for a while without problems.


Cheers,

GV