Version bump 0.5.2

Actual version bump

0.4.12 and some housekeeping

Version bump and contributors.

Merge pull request themartorana#48 from nicholasserra/nicholasserra-b…

…atch-error

Inactive Recipient error and tests

Bump to 0.4.5, add mflaxman as contributor

Update core.py

0.4.3, add Dave Peticolas as contributor