Fix compatibility with Python 3.2 (all tests pass)

In Python 3.3, a change was introduced: accessing a memoryview
element returns the correct type. In 3.2 and earlier, it always returned a bytes
object. This fix solves this issue by always converting the memoryview to a
bytes instance first. It's only a single byte, so it's not a significant
performance hit.
Update README

Add note about PyPy3 compatibility
Merge branch 'pypy3-compat' into develop
Bump version