v1.5.1

• add various MPO-MPS gate methods, including zip-up and density matrix, in the experimental submodule
• some PTensor refactoring
• Circuit: more robust parametrized gate generation
• various new contraction convenience interfaces (incld. array_contract)
• add Tensor.check() and TensorNetwork.check() for diagnostics
• add TensorNetwork.isconnected(), TensorNetwork.istree()

Full Changelog: v1.5.0...v1.5.1