v4.19.0

Features

• Experimental exact simulators built on rigetti-quax: PureStateVectorSimulator and
  DensityMatrixSimulator in pyquil.simulation._simulator. They evolve a program exactly
  under JAX, so they are jit-compatible and differentiable with respect to gate
  parameters, and they accept a NoiseModel. The API is not yet stable; see
  the architecture guide.
  (#1855)
• A gate angle may be any Quil arithmetic expression over declared memory, so the parametric
  programs quilc emits -- RX(theta[0]/2 + pi) 0 -- simulate without rewriting.
  (#1869)