It closes #4861.
It fixes playback when the rate cannot be respected (like with dvb/udp/...)
or need to be requested to the access_demux (rtsp).

It is unrelated to dvd/bd LPCM.

This is a first step to re-organize the interface, more to come

Some people find it more readable.

It allows to avoid full rgb <-> yuv conversion at a latter stage.

The shadow is enabled by default.

They should be prefixed by '#' but it is not always done...

The quality is a lot better than what we originaly had.

The placement and thickness of the underline is now global to a whole
line of text.

Created a structure to gather all informations needed to draw one character.
It simplify a bit the code.

It will be replaced by more specific options.

Outline support is temporary removed.
Underlining is a bit improved (quality and speed wise).
Overlapping over the optional background box is improved (quality wise).

There is a small regression: the alpha settings is not respected.

Unbreakables lines are now wrapped at the last non breakable space
or, if none, before the character that would make the line too large
(instead of throwing away the complete line).

Too high subtitles are now correctly truncated.

No functionnal changes.

It seems that the global one is not in synch when the callback is called.
When MT was in use, non I420 streams were broken.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>