Markdown2

- 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.

- Make the use of the `-*- markdown-extras: ... -*-` emacs-style files
variable to set "extras" **off** be default. It can be turned on via
`--use-file-vars` on the command line and `use_file_vars=True` via the
module interface.
- [Issue 3] Drop the code-color extra hack added *for* issue3 that was
causing the a unicode error with unicode in a code-colored block,
<http://code.google.com/p/python-markdown2/issues/detail?id=3#c8>

- [Issue 8] Alleviate some of the incompat of the last change by allowing (at
the Python module level) the usage of `safe_mode=True` to mean what it used
to -- i.e. "replace" safe mode.
- [Issue 8, **incompatible change**] The "-s|--safe" command line option and
the equivalent "safe_mode" option has changed semantics to be a string
instead of a boolean. Legal values of the string are "replace" (the old
behaviour: literal HTML is replaced with "[HTML_REMOVED]") and "escape"
(meta chars in literal HTML is escaped).
- [Issue 11] Process markup in footnote definition bodies.
- Add support for `-*- markdown-extras: ... -*-` emacs-style files variables
(typically in an XML comment) to set "extras" for the markdown conversion.
- [Issue 6] Fix problem with footnotes if the reference string had uppercase
letters.