Build with vapoursynth

The original concern in #1 (closed) was that Vapoursynth was big, and pulled in a lot of transitive dependencies. This is no longer the case now, as most transitive dependencies are removed, and the package itself is smaller at ~3MB installed (compared to mpv, which is ~6MB installed).

Adding vapoursynth adds 3 transitive dependencies to this package:

$ pactree -sl mpv | sort -ud > mpv.deps
$ { pactree -sl mpv; pactree -sl vapoursynth; } | sort -ud > mpv+vs.deps
$ wc -l mpv.deps mpv+vs.deps
 345 mpv.deps
 348 mpv+vs.deps
 693 total
% comm -3 mpv.deps mpv+vs.deps
        libnsl
        python
        vapoursynth

Closes #1 (closed).