Lambeq

Minor changes:
- Update install script to use PyPI package
- Add badges and link to documentation to README file
- Add lambeq logo and link to GitHub to documentation
- Allow documentation to automatically get package version
- Add keywords and classifiers to setup file

Fixes:
- Add `lambeq.circuit` submodule to top-level `lambeq` module
- Fix references to license file

Initial release of lambeq. This contains a lot of core material:

- converting sentences to string diagrams
- CCG parsing, including reading from CCGBank
- support for depccg parsing
- rewriting diagrams
- ansatze for circuits and tensors, including MPS ansatze
- support for JAX and PyTorch integration
- example notebooks and documentation