Rotate/Shift Operators Replaced w/ Fns; Type Conv for Vector Addition

The various instantiations of the rotate and shift operators were
replaced by calls to the associated functions. Necessary type
conversions were carried out in order for such functions to be
implemented. Type conversions were also implemented on specific
std_logic_vectors (those being added together) (converting from signed
to unsigned and back to signed) in order that the vectors could be added
together.