Add tests for {via, Mod, Name} registration
Add gen_process:enter_loop/3,/4

A process started with proc_lib can now enter a gen_process loop by
calling gen_process:enter_loop(Mod, Opts, State) or
gen_process:enter_loop(Mod, Opts, State, Name).
Merge pull request #3 from fishcakez/enter-loop

Add gen_process:enter_loop/3,4