extension: access special module members using sysstr
These extensions variables and mapping are module attributes so they should be
dealt with unicode `str` in Python 3. We move the part that deal with reading
theses variable and checking their validity to use unicode `str` string.
Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:
http://docutils.sourceforge.net/
Use the Makefile in this directory to generate the man and HTML pages.