Add pypy and pypy3 to travis file

Adds the pypy builds. Since everything is supposed to be super-clean
compliant python, adding support for pypy should be trivial.
Remove SHA512 speed test from testsuite

This has always been a questionable test. In fact, on the heavily loaded Travis
CI boxes, running pypy, this test fails. Apparently the pypy implementation of
sha512 is slower than the C implementation used in typical python. Not really
surprising, but it means that this test (and its implicit requirement) needs to
be dropped as we add pypy support.
Merge branch 'feature/pypy-support' into dev