Update README + setup.py and add setup.cfg + MANIFEST.in for pre-release 0.9.8

Convert README.md to README.rst for PyPI.
Update README.rst to mention non-wheel installation prior to installing tuf[tools] for pip <= 1.5.6.
Add long_description to setup.py.
Add setup.cfg.
Add MANIFEST.
Test uploaded wheel package.
Test uploaded release.