patch to compile tinydtls on Windows (MSYS2) : autoconf is found during compilation 

- add pyproject.toml to MANIFEST.in
- bump version in setup.py

 Update to devel branch

Having those in .gitignore removes clutter at `git status`, and prevents
accidental inclusion in commits.

Since 5f32f03d, its PRNG functions are fanned out into platform specific
implementations; those are included now.

force setuptools to install Cython if it's not installed

fixes setup.py

* work relative to __file__ rather than assuming that setup.py is in the
  working directory

* update the submodule (it might be practical for some cases to make
  that conditional on the submodule directory being empty)