Added initial support for command line substitution in PostProcessRecord command line.
VisionDTV user is starting ot use it to re-encode the recordings.
Just added 4 substitutions for now - 1 is PartialFileName for backwards compatibility (although I do not think that many are using it ... no-one has told me anyway) another is simply a way to put the escape character back in ($). The other 2 are the ChannelName and ChannelAssignment.
Later will probably add things like date/time of start of recording, title, series/episode and description so that people can write their own library files or populate the ID3 (or similar) tags in the re-encoded files.