Class initialization independent of the instance fetch

[alexmarincu]

Currently, the classes are initialized when calling the instance function for the first time. This is not thread-safe. In order to make it thread-safe it would require the implementation of a critical section handling (e.g. mutex lock) which would differ based on the used platform. In order to keep the framework independent of any platform the class initialization could be separated from the instance fetch. The user will be responsible for initializing the classes at the beginning of the program.