Move move builtins into SModel.C
Make builtins holder Pair.C
Move other builtins into Pair.C
Move several builtins to Prelude.C
Move evaluate and trigger to Modifiables.C
Rename builtin libraries, and also add Environment.C.
Add Environment module.
Add list of transition kernels.
Add a member function to perform transition kernels.
Add new IO action register_transition_kernel.
Add the AddMove command to the sampler Monads.