Circuit measurements should be limited to axes X, Y, and Z

[thierry-martinez]

In the discussion for #343, in particular in #343 (comment), we noticed that OpenQASM only support Z measurements.

In general, for circuits, we could limit measurements on X, Y, and Z, and give a way to reformulate them as Z measurements only.

[matulni]

Related issue: #177

[thierry-martinez]

This seems to be related to #231.