Installation and building of tools should be optional with CMake

[JayFoxRox]

I'm compiling for an embedded platform and the toolchain expects a system-wide install (so I use cmake .. -DCMAKE_TOOLCHAIN_FILE=[...] && make install).

The midifile library compiles fine.
However, compilation will still fail because the toolchain does not support some C++ features like cin which is used in tools/type0.cpp.
Because there won't be any way to run these tools I shouldn't even have to build them in the first place.

Therefore, compiling tools or examples should be made optional.
I only want to install the core library.

(I'll look for a different MIDI lib for now, but will keep an eye on this if I can't find a suitable alternative)