Added alpha version tag.

Python-Makrdown 1.7 Final.

Note that various features marked as depreciated in 1.6 have
been removed, so this release is somewhat backward
incompatible. Most notably, `str(md)` will no longer work.
`md.convert(text)` should be used instead. The `toString`
and `toUnicode` methods no longer exist. The `__unicode__`
method calls `convert` and `__str__` returns some info about
the instance rather than the converted output (although I'm
open for suggestions for improvment in the info provided).
Additionally, the `encoding` argument has been removed from
both `markdown` and `Markdown`. Markdown expects unicode (or
ascii) input and it is the users responsibility to ensure
that's what is provided. Therefore, all output is in
unicode. Only `markdownFromFile` accepts an encoding.