Relicensing to MIT/Expat license, part 1: new license document.
Relicensing to MIT/Expat license, part 2: headers.
Relicensing to MIT/Expat license, part 3: source files.
Relicensing to MIT/Expat license, part 4: CMake and documentation files.

They didn't contain license header before, but I think adding it also
there wouldn't do any harm. Some of them (UseCorrade.cmake) contain also
actual code, which also needs to be properly licensed, documentation is
also integral part of the codebase.
Relicensing to MIT/Expat license, part 5: updated package files.
Relicensing to MIT/Expat license, part 6: mention it in documentation.