Improve logging
add enqueue & perform timestamps, add job hooks for accessing them

Classes which implement the perform() method can now also implement
before_perform() and after_perform() methods which take a metadata dict.
These contain the args passed in, as well as timestamps for when the job
was enqueued and when it was performed, and whether the job failed and
was retried.
adding travis.yml
adding travis status badge
adding pypy to environments tested
tweaking readme
getting ready to remove resweb
removing resweb
updating version and manifest
temporarily removing pypy
Merge branch 'master' into remove_resweb
removing resweb script
getting ready for new release
fixing setup.py
Merge pull request #95 from joeshaw/joeshaw-timestamps

add enqueue & perform timestamps, add job hooks for accessing them
fixing failing tests
tweaking before and after perform methods
adding payload_class to both before and after perform
updating theme
tweaking job docs