Add CMake build system

[Asd-g]

• Supports building on Linux, macOS, and Windows (MSVC & MinGW).
• Builds both static and shared libraries across all supported platforms.
• Finds and links against a CMake-installed OBUParse dependency. (https://github.com/dwbuiten/obuparse/pull/16)
• Generates and installs a CMake package that provides imported alias targets for easy consumption:
  • LSMASH::static
  • LSMASH::shared
• Builds the command-line tools (muxer, remuxer, boxdumper, timelineeditor) as separate executables.
• Includes a convenient uninstall target.

Note: requires obuparse with CMake build system (https://github.com/dwbuiten/obuparse/pull/16)

[dwbuiten]

... but why? The existing build system works fine (and tbh I do not like cmake at all).

[Asd-g]

It works fine for some building environments. For others, one have to manual handle the building.