libvmaf/motion: support motion in addition to motion2

[kylophone]

Some published VMAF models require a feature called motion which is similar, but has no look-ahead like motion2. This PR adds the motion feature to both the float/integer motion feature extractors.

<VMAF version="85b492c">
  <params qualityWidth="1920" qualityHeight="1080" />
  <fyi fps="60.80" />
  <frames>
    <frame frameNum="0" motion="0.000000" motion2="0.000000" integer_motion="0.000000" integer_motion2="0.000000" />
    <frame frameNum="1" motion="4.913140" motion2="4.828127" integer_motion="4.913157" integer_motion2="4.828149" />
    <frame frameNum="2" motion="4.828127" motion2="4.678761" integer_motion="4.828149" integer_motion2="4.678786" />
    <frame frameNum="3" motion="4.678761" motion2="4.678761" integer_motion="4.678786" integer_motion2="4.678786" />
  </frames>
</VMAF>

[1480c1]

It seems the appveyor issues come from msys2/MSYS2-packages#2022, so it would be okay to ignore appveyor for now

[kylophone]

It seems the appveyor issues come from msys2/MSYS2-packages#2022, so it would be okay to ignore appveyor for now

Thanks