v2.9.0

This is a potentially breaking change.

Version 2.9.0 improves the ability to use custom ExperimentValue implementations. The previous implementation did not consider the user inheriting from this class and, therefore, did not properly handle derived types. Resolving this required changing the type from an object passed by value in places to a pointer or shared_ptr.

There were other improvements to the CMake script and various bug fixes in the examples.