Implements defclass

This fixes issue #156

Signed-off-by: Julien Danjou <julien@danjou.info>
Run unit tests against hy2py

Signed-off-by: Julien Danjou <julien@danjou.info>
Fixup comment
Merge branch 'jd/defclass' of https://github.com/jd/hy into jd-jd/defclass
Update NEWS
Correct existing tests for future try / except work.
Allow returning inside a try / except. Closes #163