v4.20.0

Features

• Helper for adding leading delays to programs with leading classical computation, including
  cases with control flow. See pyquil._qpu.add_leading_delay_to_first_pulse_block.
  (#1851)
• Support for per-shot randomized compiling on the QPU control system. The top-level
  pyquil._qpu.RandomizedCompilingConfiguration provides methods for building the necessary
  classical instructions (build_quil_program), seed values (generate_seed_values), and
  memory map values (build_memory_map) to enable the method. It additionally provides methods
  for verifying final memory read off of the QPU for verification (verify_final_memory),
  along with tracking the randomizations shot by shot (track_pauli_frames).
  (#1851)
• Support Quil shift operators. (#1851)