Modified package structure to ease adding PyPy support
Added PyPy support

Thanks @benoitc for the initial version of the patch
Added PyPy to Travis tests
Fixed running tests from the right directory
Use tox on Travis
Fixed some tests on PyPy
Separate tests
Skip unreliable tests on PyPy
Raised version and move it to __init__.py
Changed maturity to beta, YOLO
Added PyPy classifier
Updated CREDITS
Updated README