[Pydocs] Add info for Player and RenderCapture

1) Added information in comments to be pulled into PyDocs describing the
shortcomings when calling xbmc.player.getPlayingFile() for LiveTV.
Specifically that pvr:// url's are not translated into usable filenames
or streams.
2) Added information to xbmc.CapturePlayer regarding the functions
getHeight() and getWidth() which return 0 prior to calling
CapturePlayer.capture(). Also added that getAspectRatio() may be called
prior to issuing a capture() request.