Markdown2

- 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.

- Add ability for 'extras' to have arguments. Internally the 'extras'
attribute of the Markdown class is a dict (it was a set).
- Add "demote-headers" extra that will demote the markdown for, e.g., an h1
to h2-6 by the number of the demote-headers argument.

>>> markdown(' this would be an h1', extras={'demote-headers': 2})
u'<h3>this would be an h1</h3>\n'

This can be useful for user-supplied Markdown content for a sub-section of
a page.

- [Issue 18] Allow spaces in the URL for link definitions.
- [Issue 15] Fix some edge cases with backslash-escapes.
- Fix this error that broken command-line usage:

NameError: global name 'use_file_vars' is not defined

- Add "pyshell" extra for auto-codeblock'ing Python interactive shell
sessions even if they weren't properly indented by the tab width.