Transonic with Pypy3.6

It is possible to use Transonic with Pypy3.6-7.2.

pypy3 -c "import os, sys; from os.path import dirname; from _ssl_build import ffi; \
    os.chdir(dirname(dirname(sys.executable)) + '/lib_pypy'); ffi.compile()"
pypy3 -m ensurepip
pypy3 -m pip install pip setuptools -U

pypy3 -m pip install mpi4py

# in Transonic repository
pypy3 -m pip install .[test]

make coverage