Merge pull request #32 from latestrevision/sync_to_execute

Switch .sync to also utilize common _execute interface.
Support datetime objects as input.

Add tests for datetime feature.

For #33.
Merge branch 'develop' of github.com:ralphbean/taskw into develop
Update the readme.
py3 compat.
Of course, handle unicode as well as byte strings here...
Test that unicode stuff.
Serialize incoming zoned date/datetime instances into strings of the appropriate format before relaying to taskwarrior.