A skipped frame is detected when the producer offers a frame while the
current pending frame has not been consumed.
However, the producer (in practice the decoder) is not interested in the
fact that a frame has been skipped, only the consumer (the renderer) is.
Therefore, expose the skipped count in consumer_take_frame() instead of
a flag in the producer_offer_frame().
This allows to manage the skipped and rendered frames count at the same
place, and remove fps_counter from decoder.
The FPS counter was called only on new frames, so it could not print
values regularly, especially when there are very few FPS (when the
device surface does not change).
To the extreme, it was never able to display 0 fps.
Add a separate thread to print framerate every second.
Limit source code to 80 chars, and declare functions return type and
modifiers on a separate line.
This allows to avoid very long lines, and all function names are
aligned.
(We do this on VLC, and I like it.)
