Pyopenjtalk

Now that text processing frontend and speech synthesis backend are both available from pyopenjtalk.
Note that there are no API breaking changes from v0.0.x.

Demo: https://nbviewer.jupyter.org/github/r9y9/pyopenjtalk/blob/v0.1.0/docs/notebooks/Demo.ipynb

7 Embed C++ source into the repository
8 Goodbye openjtalk shared lib

- Fix an installation issue 3
- Test py37 and py38 on travis 5
- Add DOI