changed cryptic u gates to readable x and h

[rochisha0]

Summary

Fixes #1287

Changed cryptic looking u gates to readable x and h gates.
U(pi, 0, pi) --> X
U(pi/2, 0, pi) --> H

Details and comments

[Cryoris]

Nice! There are a few more we can update:

• In reciprocals we have cu(2 * np.pi, 0, 0, 0, q0, q1) which is the same as cry(2 * np.pi, q0, q1)
• In some places we have p(pi/4) which is the same as t and p(-pi/4) which is the same as tdg
• Similarly p(pi/2) is s and p(-pi/2) is sdg

[rochisha0]

Done @Cryoris !

[woodsp-ibm]

Thanks for the contribution which makes reading the circuits easier.