DeepXDE v1.6.0

Backend JAX supports PDE inverse problems.🎉🎉🎉

Areas of improvement

• Backend PyTorch supports l2 regularization
• Improve XLA jit

New APIs

• Add dde.data.PDEOperatorCartesianProd
• Backend TensorFlow supports dde.nn.PFNN

API changes

• Model.train: epochs is replaced by iterations
• Merge PIDeepONet into DeepONet