Improve compability with AviSynth+
v210 input support

Assembly based on code by Henrik Gramner and Loren Merritt.
Add support for AVC-Intra Class 200
Auto keyint

When --keyint is negative value or "auto", keyint_max is set to fps * 10 automatically.
Merge branch 'plain' into 7mod

Conflicts:
	encoder/encoder.c
	encoder/set.c
	input/raw.c
	input/y4m.c