Feature release 0.9.0

Added

• QGymMapper mapper pass
• U(theta, phi, lambda) gate to default single-qubit gates
• Z90 and mZ90 pi-half rotation gates (equivalent to S and Sdag gates)
• Operation duration in terms of execution cycles can be specified for the QuantifySchedulerExporter
• measurement_to_bit_map property added to the Circuit class

Changed

• Circuit.export expects an Exporter instance as input argument (instead of an ExportFormat)
• Moved Bloch sphere rotation composition from the merger pass interface to Bloch sphere rotation semantic module
• Refactor gate semantics as attributes of gates

Removed

• The QuantifySchedulerExporter no longer returns a bit_register_mapping
  (use Circuit.measurement_to_bit_map property instead), it only returns a quantify-scheduler Schedule
• The ExportFormat has been deprecated
  (exporters can be specified by providing an instance as input argument to Circuit.export)