Convert .py files to .md

A module (or package) to convert `scientific_python/*/*.py` files to [Markdown](https://en.wikipedia.org/wiki/Markdown) `.md` files should be prepared. Also Cython `.pyx` files can be included to the list of converted files. The proposal of conversion rules is located in [`misc/book/py_format.md`](https://github.com/hombit/scientific_python/blob/master/misc/book/py_format.md)