* Limit max size of preview to the timeline size (this renders very small profiles correctly)
* Fixing CRF quality setting to allow "low" quality without breaking
* First implementation of CRF (Constant Rate Factor)
* Include AV1 in the codecs that can use crf
* First version that uses SetOption to set crf quality
* Clarify comments
* Delete setting the bitrate for crf in SetVideoOption because it
is not needed, it is set later with SetOptions.
* FFmpeg4 support. Compile warnings fixes. Credit goes to many people, including ferdnyc, peterM, and other awesome folks!
* Adding environment checking to enable/disable omp taskwait after each video/audio frame is processed. This is experimental for some users with crashes.
* Moving `omp taskwait` to after the ProcessVideoPacket() method, since that is the only place it is useful.
* Fixing crashes on missing Clip source file, and changing FFmpeg scaling algorthm from SWS_BILINEAR to SWS_LANCZOS (for higher quality scaling)
* Update FindFFmpeg.cmake module, and updating build script. Also enabling debug builds.
* Updating experimental travis build script
* Fixed unit test for newer version of FFmpeg (audio resampling)
* Experimental travis multiple jobs
* Adding OMP schedule hint (thanks PeterM), which prevents crashes in some circumstances.
* Adding strict experimental to FFmpegReader and Writer (hopefully allowing all the encoders to be used)
(cherry picked from commit 1bcd1e5)
* init all formats and codecs before checking if valid
(cherry picked from commit 7250226)
