Rotation Gates

[sagnikpal2004]

Rotation Gates are not available in QuantumSymbolics.

I have implemented Rotation Gates in a fork: https://github.com/sagnikpal2004/QuantumSymbolics.jl/tree/rgate
I have tested the feature, and it works well. The unit tests also pass.

Here is its usage:

using QuantumSymbolics

express(Rx(1.0*pi))
express(Ry(1.0*pi))
express(Rz(1.0*pi))

express(RGate(:x, 0.5*pi))
QuantumSavory.apply!(reg[1], Ry(0.25*pi))

Let me know if this is something that can be merged into QuantumSymbolics

[apkille]

Looks like a nice addition to me! In my opinion, RotationGate would probably be a clearer name than the abbreviated RGate, but this can be discussed in a pull request. Could you please submit a PR?