Fix broken links in GEMPAK Comparison Guide
Fix broken links in GEMPAK Comparison Guide

Apparently at some point the api directory moved from being a
subdirectory of the userguide directory to a sibling directory.  In
addition, a few links had a duplicated generated directory.

I didn't test every single link, but the ones I did try all work with
these changes.

Unidata/MetPy,Unidata/MetPy