Better XMLTV integration for tvdb_augment_data

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At the moment the info provided by tvdb_augment_data is a huge mass of text in MythTV, much of it redundant, which makes it a little difficult to parse. It'd be nice if it could better integrate its data into the XML, eg:

1. Often the "Overview" from TVDB.com is at least partially identical to that already grabbed. Eg see the example below. Ideally the postprocessor should only add new text, not duplicate a description we already have.
2. The list of "Actors" is usually identical to what's already listed under <credits>. Also we shouldn't put this information in the <desc> tag. Ideally we would check each actor against what we've already got in the XML, and add any new ones to that field, keeping <desc> free of such info.
3. The "FirstAired?" field should be stored in <date>, not <desc>.
4. The "Genre" field (not in example below, but in others) should be a <category> field (probably validated against Shepherd::Common), not part of the <desc>.
5. The "EpisodeNumber?" field should be in an <episode-num> tag.
6. Doesn't seem to be any point in including "EpisodeName?" in the <desc>, since that's identical to <sub-title>.
7. "ShowURL" should be in an <url> tag.
8. Doesn't seem any point including "Status", since that's American-specific.
9. Is there any way of identifying Australia variants of American shows? E.g. "Big Brother" is augmented with a lot of info that's specific to the American version. Perhaps make "Network" more prominent, so you can see it's data about a CBS show?
10. Kind of a shame we can't put some kind of <star-rating> in there, since I think that'd actually be useful info. I know if there's a new show coming up I'd like to see what other people have rated it.
11. None of the line breaks are preserved within MythTV. Not sure if we can do anything about this, but it's just a mass of text which is not easy on the eyes.

Many of these points also relate to imdb_augment_data. Perhaps they could share a common Shepherd::Something library.

  <programme start="20070608002500" stop="20070608012000" channel="abc.free.au">
    <title lang="en">Red Cap</title>
    <desc lang="en">Written by Patrick Harbinson (ER, Dark Angel), Red Cap, set on a British base camp in Germany, focuses on the elite plain-clothe
s detective unit of the Royal Military Police. Known as the Special Investigation Branch, the SIB is charged with one of the most demanding of all m
ilitary jobs: the investigation of serious crimes committed by, or against, members of the British Army.

TheTVDB.com augmented data:
Series Info:
 Overview: Welcome to the Red Cap guide at TV Tome.   Written by Patrick Harbinson (ER, Dark Angel), Red Cap, set on a British base camp in Germany,
 focuses on the elite plain-clothes detective unit of the Royal Military Police. Known as the Special Investigation Branch, the SIB is charged with 
one of the most demanding of all military jobs: the investigation of serious crimes committed by, or against, members of the British Army.  Sergeant
 Jo McDonagh (Tamzin Outhwaite) is a tough-talking, dedicated new recruit to the unit, who has just been transferred to the SIB from the Close Prote
ction Unit. Jo is a maverick who has to prove herself and gain acceptance in a man's world that is suspicious and unwelcoming towards outsiders. Red
 Cap was made with the full cooperation and support of the British Army.
 Status: Ended
 FirstAired: 2003-01-01
 Network: BBC-1
 Actors: |Nigel Harman|Tamzin Outhwaite|Blake Ritson|Maggie Lloyd-Williams|James Thornton|Douglas Hodge|Raquel Cassidy|Gordon Kennedy|Peter Guinness
|</desc>
    <credits>
      <actor>Tamzin Outhwaite</actor>
      <actor>Douglas Hodge</actor>
      <actor>James Thornton</actor>
      <actor>Nigel Harman</actor>
      <actor>Blake Ritson</actor>
      <actor>Maggie Lloyd-Williams</actor>
      <actor>Raquel Cassidy</actor>
      <actor>Gordon Kennedy</actor>
      <actor>Peter Guinness</actor>
    </credits>
    <category lang="en">Crime Drama</category>
    <category lang="en">Drama Group</category>
    <rating>
      <value>M</value>
    </rating>

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Done, more or less.