[projectm] Add new port

[kblaschke]

• Changes comply with the maintainer guide.
• The name of the port matches an existing name for this component on https://repology.org/ if possible, and/or is strongly associated with that component on search engines.
• Optional dependencies are resolved in exactly one way. For example, if the component is built with CMake, all find_package calls are REQUIRED, are satisfied by vcpkg.json's declared dependencies, or disabled with CMAKE_DISABLE_FIND_PACKAGE_Xxx.
• The versioning scheme in vcpkg.json matches what upstream says.
• The license declaration in vcpkg.json matches what upstream says.
• The installed as the "copyright" file matches what upstream says.
• The source code of the component installed comes from an authoritative source.
• The generated "usage text" is accurate. See adding-usage for context.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is in the new port's versions file.
• Only one version is added to each modified port's versions file.

Second attempt on adding a portfile for the projectM Music Visualizer library, now using the recently added projectm-eval port as a dependency.

The port has an optional feature, "boost-filesystem", which can be enabled to use Boost instead of the C++ STL to implement portable filesystem support. When used on toolchains without C++17 support, this feature must be enabled by the user. As there's no way to check this automatically before the need to enable it, the portfile will emit a message to the user instead:

-- If your current vcpkg target triplet or toolchain does not support C++17 or lacks std::filesystem support, please enable the "boost-filesystem" feature.

[WangWeiLin-MV]

The port features usage tests pass with the following triplets:

• x64-linux
• x64-windows