Use proper keyword when linking libraries with CMake

[lucasmyers97]

When you link libraries with CMake you must include a PUBLIC, PRIVATE, and INTERFACE keyword. I am unsure which to use when, but it appears that if I use PRIVATE then oftentimes the include directories are not linked downstream so that it throws an error when trying to include a file from a dependency (which is more than one node up the graph). In this case I don't really understand the use of the keywords, but I think using the proper one must be important for good software design.

[lucasmyers97]

Should still go through this, but this comment should clarify: From the CMake documentation

"Generally, a dependency should be specified in a use of target_link_libraries() with the PRIVATE keyword if it is used by only the implementation of a library, and not in the header files. If a dependency is additionally used in the header files of a library (e.g. for class inheritance), then it should be specified as a PUBLIC dependency. A dependency which is not used by the implementation of a library, but only by its headers should be specified as an INTERFACE dependency. The target_link_libraries() command may be invoked with multiple uses of each keyword"

Basically:

• Use PRIVATE when the linked entity is only used in the .cpp file.
• Use PUBLIC when the linked entity is used in the .hpp and .cpp files
• Use INTERFACE when the linked entity is only used in the .hpp file.