Pyxtal

A major release with the following highlights:

- Implementation of pyxtal.optimize module to allow automated organic crystal structure sampling (see more instructions in [HTOCSP](https://github.com/MaterSim/HTOCSP))
- Allow the support of random number generation with the fixed seeds and many other code re-factorization 267
- Update of calculators in pyxtal.interface

- Improve the database function as well as gulp/dftb calculators
- Add the function to apply chemical substitution from one element to two elements (e.g., from C to BN) 259

- Fix k-group splitting 252
- Improve database function
- Add tab_representation
- Add space group representation 250
- Improve wyckoff_position class 253 251

- Improve the site-symmetry notation 249
- Improve the handling of smiles string and representation for molecular crystals.

- update the get_transition function (247 248)
- Improve the get_1D_representation function
- update pymatgen dependency

Enabled the get_forcefield function