Patch searchio doc

Per http://lists.open-bio.org/pipermail/biopython/2013-February/008324.html

I changed some of the SearchIO language style and added actual links to the example files and documentation pages.

Links to the documentation pages are 404 at the moment, as the pages haven't been created (I assume they will be there after 1.61 is released).

Anyway, hope I didn't miss anything :).