Markdown2

- Fix syntax_color test for the latest Pygments.
- [Issue 20] Can't assume that `sys.argv` is defined at top-level code --
e.g. when used at a PostreSQL stored procedure. Fix that.

- Fix sys.path manipulation in setup.py so `easy_install markdown2-*.tar.gz`
works. (Henry Precheur pointed out the problem.)
- "bin/markdown2" is now a stub runner script rather than a symlink to
"lib/markdown2.py". The symlink was a problem for sdist: tar makes it a
copy.
- Added 'xml' extra: passes *one-liner* XML processing instructions and
namespaced XML tags without wrapping in a `<p>` -- i.e. treats them as a HTML
block tag.

- Fix bug in processing text with two HTML comments, where the first comment
is cuddled to other content. See "test/tm-cases/two_comments.text". Noted
by Wolfgang Machert.
- Revert change in v1.0.1.6 passing XML processing instructions and one-liner
tags. This changed caused some bugs. Similar XML processing support will
make it back via an "xml" extra.

- License note updates to facilitate Thomas Moschny building a package for
Fedora Core Linux. No functional change.

- Add a proper setup.py and release to pypi:
http://pypi.python.org/pypi/markdown2/
- Move markdown2.py module to a lib subdir. This allows one to put the "lib"
dir of a source checkout (e.g. via an svn:externals) on ones Python Path
without have the .py files at the top-level getting in the way.

- Fix Python 2.6 deprecation warning about the `md5` module.
- Pass XML processing instructions and one-liner tags. For example:

<?blah ...?>
<xi:include xmlns:xi="..." />

Limitations: they must be on one line. Test: pi_and_xinclude.
Suggested by Wolfgang Machert.