openfx-io for Natron 2.4.1

What's Changed

• Misc. typo fixes by @luzpaz in #3
• sync ReadFFmpeg with mov64Reader 12.2v5 by @devernay in #5
• WriteFFmpeg: sync with 12.2v5 by @devernay in #6
• WriteOIIO: do not add "Color." to the channel names of the color plane by @devernay in #7
• GenericWriter: do not unpremult/premult before/after colorspace change. by @devernay in #8
• cmake & appveyor support by @devernay in #9

New Contributors

• @luzpaz made their first contribution in #3
• @devernay made their first contribution in #5

Full Changelog: 1.2.1...Natron-2.4.1