Include more meta data for movies.

Movie year, length and star ratings are now included in the output when
it is present in the source data.
Include part number meta data for multipart programs.

This commit also includes more robust season/episode data parsing.
Add support for 'premiere' and 'new' metadata.
Add support for program ratings.
Add support for audio properties.
Improve parsing for ratings.

It seems there is a 'contentRating' field in the program detail and a
'ratings' field in the schedule. Previously I was only checking the
'ratings' field, now I first check the 'contentRating' field.
Include callsigns and channel numbers in output.

The XMLTV schema does not seem to have direct support for these. However
it seems MythTV assumes the first three 'display-name' elements are
name, callsign and channel number so I am following that scheme for now.