y_serial_v070.py certified to run under Python 2.7.8 and IPython 2.3.0

Henceforth character set for yserial will assume utf-8.

Tags MAJOR shift from Mercurial-hg mirror to pure git.

No further dependence on the Mercurial hg-git extension.
The hg files are deleted. Some tag history remains.

Supplement repo with GitHub specific docs like:
CONTRIBUTING.md and README.md in Markdown.
Previously used rst format.

created stable branch and v060 tag.

--HG--
branch : stable