Rename `postMultiply` to `postmultiply` before release

[TysonRayJones]

for improved visual clarity! Then the first capital letter in a function name consistently disambiguates the "thing" being operated. E.g.

applyMultiQubitProjector
multiplyMultiQubitProjector
postmultiplyMultiQubitProjector

[TysonRayJones]

Revised rename proposal:

• applyMultiQubitProjector
• preapplyMultiQubitProjector
• postapplyMultiQubitProjector

[TysonRayJones]

Yet another revision:

• applyMultiQubitProjector()
• leftapplyMultiQubitProjector()
• rightapplyMultiQubitProjector()

[TysonRayJones]

Offline thoughts for posterity:

Consider a density matrix rho and an operator V. QuEST now has API functions to discretionarily effect:

V rho V^dagger
V rho
rho V

The latter two are useful when building QIT subexpressions, like commutators. The tentatively named functions to perform these (letting V = CompMatr) are respectively:

applyCompMatr()
multiplyCompMatr()
postmultiplyCompMatr()

I've become dissatisfied with this naming. My reservations are:

• "multiply" doesn't really delineate the function semantically; it's "tensored-multiply" if anything but such a thing is also a constituent of "applying"
• "multiply" is visually similar to the "Multi" morpheme, leading to visually noisy names like multiplyMultiQubitProjector()
• "multiply" and "postmultiply" are not on the same footing although I'd argue their relevance in QIT is equal
• "postmultiply" is quite a long prefix!

Feedback from Simon, Richard, Oliver and Balint indicated that preapply and postapply sounded "temporal" and that leftapply and rightapply suited better.