clean up epmgp.py

[mmahsereci]

it is not easy to read. Also we might want to move it out of the util folder

[apaleyes]

Moved epmgp to a more appropriate place. The code there seems to follow the paper notation very closely, so that may as well stay as it is. But for the functions this package defines we should at the very least have types and docstrings. @aaronkl would you be able to help write those docstrings?

[aaronkl]

sure I can do that