convert: use bytes for value in extra dict
The keys and values of the extra dict are expected to be bytes. Before this
fix, there was a crash in mercurial.changelog.encodeextra().
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.