Install ffmprovisr recipes into FFCommand Engine

The command installs a flavour of the current FFmpeg recipes, as discussed in ffmprovisr, into the FFCommand Engine. Currently this command works on macOS and Windows Terminal or Subsystem for Linux.

Note that the binaries of FFCommand Engine available on the GitHub website are version 0.51 for macOS and 0.5 for Windows, but the uncompiled code is of version 0.6. We have released a Homebrew formula which installs the version 0.6 on macOS. We plan to modify the formula to work also on the Windows Terminal and Subsystem for Linux. In addition, we plan to program a Makefile for Linux.