lwindex: Fix a C++ compilation.
Update VapourSynth.h to synchronize with R21.
lwindex: Construct frame from pair of field coded picture automatically if any.

This is not invoked when output order is unknown or broken.
libavsmash: Support High Efficiency Video Coding.
lwindex: Generate PTSs from POCs for HEVC stream if incomplete.
libavsmash: Try to get codec_id from summaries when getting track if unknown.
lwindex: The maximum max_num_reorder_pics is equal to 15 for HEVC ver.1.
Merge https://github.com/VFR-maniac/L-SMASH-Works
Add VC12 support.
vslsmashsource: Don't print any info from libav/ffmpeg.