Add QROT and MS gate

[BoxiLi]

Add the QROT gate class.

[BoxiLi]

Hi @ajrazander Would you like to have a review?

Does this definition of single-qubit rotation make sense? Or is there a better name than QROT?

[ajrazander]

The gate looks good! The QROT name could be improved. In the literature it's usually referred to as just R. I kind of like that as it fits with the naming scheme that already exists for the Rx, Ry, and Rz gates. Using R would also put it in the list of gates near the Rx, Ry, Rz gates which would make searching for it easier and more recognizable for new users.