FindMagnum: fixed formatting with `cmake --help-module`.
Doc++
Updated and polished coding style documentation.
Updated FindCorrade.cmake from Corrade repository.
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.

Added license header also to shader sources. Hopefully it won't harm
compilation times too much.
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. 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.