v0.4.0

Improvements and Changes

• Updated requirements.txt and setup.py files (gh-83)
• Added support for chi superoperator conversion and augmented documentation for
  superoperator representations (gh-76)
• Renamed superoperator_conversion to superoperator_tools (gh-100) to reflect
  new functionality, including helpers to apply a Choi process to a state, compute
  the Pauli twirl (gh-101), testing properties (e.g. CP, TP) of channels in the Choi
  representation (gh-109), and projecting Choi matrices to nearby processes satisfying
  those properties (gh-114)
• Following update to pyQuil version 2.7.2, changed stddev to std_err and removed qubits
  argument when using pyquil TomographyExperiment (gh-107)
• Changed the default input basis from SIC to Pauli for process tomography (gh-105)
• Standardized around use of pyquil.gate_matrices for definitions of gate matrices (gh-103)
• Added support non-square Kraus operators to superoperator conversion tools (gh-102)
• Renamed diamond_norm to diamond_norm_distance gh-104
• Made use of superoperator tools wherever possible throughout the repo (gh-111)
• Standardized around use of dim as variable name for dimension (gh-112)
• Added entanglement_fidelity calculation in distance_measures.py (gh-116)

Bugfixes

• Fixed keyword argument name symmetrize_readout in call to pyQuil's
  measure_observables (gh-115)