- support pypy3
- added contextmanager, ContextDecorator
- added (log|print)_(enters|exits)
- print stack trace in (log|print)_(calls|errors)
- added label argument for tap()
- better formatted call signatures in debug utilities
- added itervalues()
- exposed empty(), iteritems()
- exposed wraps and unwrap()
- slightly optimized last() and nth()
- fixed signatures of functions wrapped with wrap_(mapper|selector)