getSpecies was defined in two translation units. This was not an issue
for regular builds but broke unity builds. this has been refactored to a
single function in utils.h
also added ability to use Compositions as a std::hash in unordered_* types. Further added a constructor to build a Composition from a const CompositionAbstract&
MaskedComposition is a generally useful decorator, therefore instead of forcing callers to impliment it on their own, we have implimented it as part of libcomposition
It is sometimes useful for callers to be able to create new composition objects without overloading all the required methods. The CompositionDecorator acts as a simple translation layer which will pass any calls to virtual methods down to the next level of the composition stack (other than those which may have been overloaded by the caller)
