Don't install headers that aren't part of SLEIGH core

[tetsuo-cpp]

At the moment, this CMake wrapper only builds the core part of SLEIGH but omits some optional components. However, the installation includes headers for those optional parts.

So if an application using SLEIGH tries to use an optional component, it will compile fine since the header exists in the installation but will hit an error at linking time. To solve this, we should only install the headers that we can use.

The relevant part of the CMake configuration is here:

sleigh/CMakeLists.txt

Line 57 in 5e0acc7

FILES_MATCHING PATTERN "*.h*"

[tetsuo-cpp]

As of f524fa3, this is no longer relevant.