Complete cmake build and Linux support

[Janrupf]

This PR fully moves the build system to CMake. This mainly concerns Windows where it has been more difficult to build the project.

This should simplify building the project by a lot. On Windows CMake takes care of automatically providing everything required for building FFMPEG, including downloading NASM and Busybox if required.

This PR is based on some commits of https://github.com/ambrosiogabe/MathAnimation/pull/47

What this PR does:

• Add Linux support
• Move everything to CMake, entire build is automated
• Supports multiple CMake generators (VS, Ninja, Unix Makefiles)

What this PR does not do:

• Fix a bunch of compiler warnings
• Enable any further optimizations
• Improve usability on Linux

These things should be added in further PR's to avoid bloating this more.

Note's on Windows: The build of FFMPEG has been fully integrated into CMake and should happen automatically now. This needs to be tested, as it requires some rather extensive wrapping and emulation of a small Unix like environment.

[ambrosiogabe]

Hey thanks for the PR @Janrupf ! I've taken a brief look and it looks great. I'll probably have time later tonight to give it a more in depth look and just test it real quick locally, but I don't anticipate running into any problems. I'll leave an update when I get a chance to check it out :)