Fix compile error with 3.8

Replace optparse by argparse

Positional-only code generation optimization

Make pythran version checks more resilient

Add PEP420 namespace support.

Call ".tp_repr()" instead of ".tp_str()" when formatting builtin types, since it avoids an indirection in Py3.8.

Current checks breaks when setting 0.10.0 as a Pythran version :-/

Add PyBytes_FromObject() and PyObject_Bytes()

Closes GH-2936.

Closes GH-2939.