Spectrally-regularised-lvms

* The license file was added to all `.py` files in the repository.

* Bumped the Poetry version was v2, added type hints were added to the codebase, Zenodo was incorporated, and GitHub actions were defined for easier releases.

* Focused on the documentation, improved the symbolic functions, added ability to use finite difference approximations to gradient and hessian, updated function arguments and class names to be more consistent. Changed LinearModel to accept the time-series signal as an input so that users do not need to perform hankelisation. Overall just general QoL changes.

* Updated docs, README.md, and added 'whitening' flag for NegentropyCost instances.

* First PyPi publication of the package.