lavfi/afade: use standard options parsing

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/noise: use standard options parsing

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/blend: use standard options parsing

Signed-off-by: Paul B Mahol <onemda@gmail.com>
doc: move ffmpeg-codecs.texi content to separated file

This should simplify inclusion in monolithic tool manuals.
doc: move ffmpeg-formats.texi content to separated file

This should simplify inclusion in monolithic tool manuals.
doc: move ffmpeg-devices.texi content to separated file

This should simplify inclusion in monolithic tool manuals.
doc: move ffmpeg-resampler.texi content to separated file

This should simplify inclusion in monolithic tool manuals.
doc: move ffmpeg-scaler.texi content to separated file

This should simplify inclusion in monolithic tool manuals.
doc: enable compilation of -all tool pages

In particular, add documentation configuration system, through the
doc/config.texi file.

Fix trac issue #2374.
cmdutils: remove error message from opt_default() in case of missing option

A similar error message is generated by the calling function, avoid
duplication and spurious error message occurring with negated boolean
options introduced in 8bb5680, which can be reproduced for example with
the command:
ffmpeg -f lavfi -i testsrc=d=0.1 -nostdin -f null -