Switch show & episode parsing to expat w/improvements.

I changed the calls that return a show and/or (an) episode(s) to use the
expat parser.  In my testing of the full Jeopardy! data (about 2.4M worth
of show + episodes) the old code took about 1.8 seconds, while the new
took 0.6 seconds (both were parsing a local, uncompressed xml file).  I
also switched the get_show_and_episodes() call to download the zip data,
which will save a lot of bandwidth (e.g. that 2.4M of Jeopardy! data is
only 77K, for instance).  To add the latter feature I needed a language
abbreviation, so I added the ability to specify the language to the
TheTVDB constructor (which defaults to "en").
Got rid of the Show and Episode classes.

The Show and Episode classes were removed, returning their XML data in
an attribute hash.  A few unused functions were also removed.