Deepmd-kit

The very first alpha release of deepmd-kit version 2.0.0. It includes the following new features
- Model compression
- New descriptor: three body embedding
- Hybridization of descriptors
- Long-range modification
- Type embedding (under development)
- Training and inference the dipole (vector) and polarizability (matrix). (under development)
- Split of training and validation dataset. (under development)
- ROCm device support (under development)

Enhancements
- More efficient training: all customized OPs are implemented with GPU.
- Parallel training with multiple GPU support (under development)

Improvement of the code for developers
- Supports version of the model. Easily check model compatability
- Clear and pythonic python interface
- C++ API that can be tested independently
- OP supports multi-device.

Bug fixings:
- remove `using namespace std`. Solves compiling compatability problem.
- added `deepmd` namespace for the C++ API

New features:
- Atom type embedding
- Model deviation for virial

Enhancement:
- Improved documentation
- Better support for dipole and polarizability learning
- bit operations to encode neighbor information
- MPI support for atomic model deviation 628
- UT for GPU code 569
- UT for model compression 586
- Test Lammps build 600

Bug fixings
- cuda memory access error 566
- relative force model deviation is not copied back at single precision 599
- correct way of allocating memory in float precision 612
- fix TB logdir remove bug 617
- Append out_file when lammps restarts 640

- Training and inference the dipole (vector).
- Split of training and validation dataset.

Enhancement:
- Strict argument check in the input script.
- Update readme for v2.0
- Auto conversion of input file to v2.0 compatibility

Bug fixings:
- Fix bugs of broken examples.

Bug fixing:
- Fix lammps memory leak when initialized pair_style deepmd for multiple times. 392
- Fix GPU memory issues. 393 407 424