configure: change to use /bin/sh
Update to current libav/ffmpeg API
Replace gf_malloc with regular malloc in mp4 muxer

It was used as a workaround for a bug that only existed in the GPAC repository
for a few weeks back in 2010. There's no reason to keep it anymore.
Use calloc instead of malloc + memset
x86inc: Make ym# behave the same way as xm#

This makes more sense for future implementations of templates with zmm registers.
CRF-max: don't warn if VBV underflow occurs

Only warn if underflow occurs for reasons other than CRF-max, as CRF-max
implies that VBV underflow is desired by the user.
chroma-me: take shortcut in BI analysis

~100 cycles faster with subme>=9
Add --filler option

Allows generation of hard-CBR streams without using NAL HRD.
Useful if you want to be able to reconfigure the bitrate (which you can't do
with NAL HRD on).
Add AVC-Intra 1080p50/60 Class 100 parameters

Also add some compatibility fixes.
Add L-SMASH support as preferable alternative for MP4-muxing