[IMP-dev] documentation suggestion

The IMP doxygen documentation currently throws a lot of class and function names in your face in no particular order (well, alphabetical, but no conceptual order). We can use doxygen modules to give it a nicer structure. This patch adds a module for logging and another for error checking. I think they help a lot. We probably want ones for - Restraints - Optimizers - States - The kernel - Decorators - random helpers - internal stuff

To create a module put a \defgroup id Pretty name with spaces in some doxygen comment and to add something to one put a \ingroup id in the objects commnets