v0.1.5:

- Now using `Optional` in type annotation;
- No-relaxation option in `sims.blochsim` by inputting `T1=None, T2=None`:
  slightly faster `forward` and `backward` computations;
- Bug fixes in `slowsims.blochsim` when `T1=None, T2=None`;
- Added `doRelax` option to `applypulse`;
- Temporarily removed `cupy` from dependencies, in case it causes issues during installation;
- Added html documentations and link to arXiv.