Address trac ticket #2431.

This reverts commit 580ee973.

Sample has been forgotten, revert this commit in a day or two, when
sample is available everywhere.

Note that the linebreaks text codec option (but not the feature) has
been removed; its main goal was to allow demuxers to configure the text
decoder (and not meant to be used by users), but the AVOption are not a
viable solution. This is solved differently in this commit.

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>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

This change introduces a basic encoder for 3GPP Timed Text subtitles,
also known as TX3G, Quicktime subtitles, or "movtext" in the existing
code.

This initial change doesn't attempt to write styling information,
and just writes the plain text of the subtitles. I intend to add
support for styles eventually, but it's challenging due to a lack
of existing players that support them.

Note that an additional change is required to the mov/mp4 muxer to
write empty subtitle packets to indicate subtitle duration.
Signed-off-by: Philip Langdale <philipl@overt.org>

This change introduces a basic decoder for 3GPP Timed Text subtitles,
also known as TX3G, Quicktime subtitles, or "movtext" in the existing
code.

This initial change doesn't attempt to parse styling information,
and just reads the plain text of the subtitles. I intend to add
support for styles eventually, but it's challenging due to a lack
of existing players that support them.
Signed-off-by: Philip Langdale <philipl@overt.org>