The SRT muxer is reponsible for separating events with two line breaks,
there is no need to add more than necessary. Similarly, other muxers
(such as Matroska) are not supposed to add line breaks at the end of the
payload.
Unsurprisingly, if a timing-less subrip decoder is desireable, an
encoder is as well. With this in place, we can move on to remove
the use of the old encoder/decoder with embedded timing and move
all timing handling the (de)muxer where they belong.
Signed-off-by: Philip Langdale <philipl@overt.org>