Py-ubjson

- Make recursion unit test work in PyPy also

- Don't use C extension under PyPy. (JIT-optimized pure-Python version is
considerably faster.)

- Fix decimal encoding bug/assert (reported by mgorny)

- Fix DecoderException not including offset when C-extension in use, expose
property for it.
- Fix decoding via C extension reading too much data from file-like objects
- Test suite exercises both pure & extension modules when extension enabled
- Expand test suite to increase C extension (line) coverage
- Remove need for pypandoc/rst (use original README.md)
- Fix spelling errors in cli util (hoenn)

- Make extension build more reproducible with sorted sources (bmwiedemann)
- Fix _ubjson_decode_value case statement fallthrough and use correct check
to not re-raise existing decoder DecoderException

- Relax floating point type test case (for 32-bit targets)
- Added Python 3.7 to classifiers list