Added

• UnitarySimulator backend for computing the unitary transformation corresponding to a quantum circuit

Changed

• Moved some exceptions classes into their own files to avoid code duplication

Deprecated

Fixed

• Prevent infinite recursion errors when too many compiler engines are added to the MainEngine
• Error in testing the decomposition for the phase estimation gate
• Fixed small issue with matplotlib drawing backend
• Make all docstrings PEP257 compliant

Removed

• Some compatibility code for Python 2.x

Repository

• Added isort to the list of pre-commit hooks
• Added some more flake8 plugins to the list used by pre-commit:
  • flake8-breakpoint
  • flake8-comprehensions
  • flake8-docstrings
  • flake8-eradicate
  • flake8-mutable