Preparation for PyPI registration

- Since PyPI doesn’t support Markdown but reStructuredText instead, I converted the readme file from Markdown to RST.
- For PyPI release it has to be versioned so I also decided an arbitrary version: 0.1.0.  Of course it can be changed in setup.py script.
- For script installaton, there are a standard but less portable way and a de facto standard but more portable way:
    - [`scripts`][1] is provided by `distutils` which is a part of Python standard library.  It is everywhere Python is installed, but doesn’t work well with Windows.  `warp.py` is installed in Python `bin`.
    - [`console_scripts`][2] is provided by `setuptools` which is a de facto standard package manager.  It is nearly everywhere Python is installed and everywhere `pip` is installed.  It works way better than standard `scripts` with Windows.  `warp` is installed in Python `bin` if `setuptools` is available, or you have to use `warp.py` command instead.

[1]: https://docs.python.org/3/distutils/setupscript.html#installing-scripts
[2]: https://pythonhosted.org/setuptools/setuptools.html#automatic-script-creation