Made the benchmark run with no additional prep (other than installing the requisite alternative implementations).

Updated to Discount 1.3.1.

* Include the ext/VERSION file in the gem, as it's required for building.
* Added a benchmark script

Handle the 'tidy' library not being installed.

* Cleaned up a bunch of stuff from the first version.
* Initial whack at README/RDoc updates
* Trying a new hack to figure out what file extension libtidy might have on
any platform. This will work under MacOS X and FreeBSD; needs testing under
other platforms.
* Pass the flags to the allocator so MKD_NOHEADER is applied.
* Removed some options that aren't useful with the way the extension works, or which
don't seem to behave as advertised.
* Renamed :strip_html option to :escape_html as it's a more-accurate description of what it's
actually for.

* Checkpoint commit of MarkdownTest integration

- Renamed tests without goofy numbers.