dfa: implement missing TDLT coding method
lavfi: switch to an AVOptions-based system.
lavf: add libquvi demuxer.
Merge commit 'b439c992c23f3e0f3832fffd2a34a664b236c525'

* commit 'b439c992c23f3e0f3832fffd2a34a664b236c525':
  lavfi: switch to an AVOptions-based system.
  dfa: implement missing TDLT coding method

Conflicts:
	libavcodec/dfa.c
	libavfilter/avfilter.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
lavu/eval: rename "new_eval_expr()" to "make_eval_expr()"

The new name is more semantically and stilistically consistent.
lavfi/overlay: add dynamic expression evaluation support

Add support for dynamic x, y expressions evaluation.

Also add support for an evaluation mode which allows to disable per-frame
evaluation, so that there is no speedloss in case the expression does not
depend on frame variables.
lavfi/overlay: add enable expression

This expression is useful to enable/disable overlaying on the fly.

Note that this can't be easily done relying on the filtergraph structure,
since this implies caching issues or a null frame overlaying in the best
case, which is better avoided for performance and convenience reasons.
lavfi/overlay: add process_command callback