Doc + Meta fixes.

Use meta  in Makefil.PL to add repo links. They will be honored by CPAN search engines.
PPM docs:
    - Randy Kobes passed away on Sept 2010. theoryx5 won't be getting any further ppm updates.
    - stein.cshl.org/ppm is also outdated and does not have builds for recent perls
    - Mention up-to-date ppm repos instead.
libgd project was moved over to libgd.org/bitbucket
Mention automatic build tools for Mac