Update changelog for 1.3.0

I added everything I did for the CPAN/Perl package support, and mentioned the Python 3 compatibility tweaks. I also made every bullet capitalized for the entire changelog, because the inconsistency was bugging me. :smile:

Oh, I also changed the version of the next release to 1.3.0 from 1.2.2, since it has major new features now.
Merge pull request #66 from dan-blanchard/patch-2

Update changelog for 1.3.0