Template-nn

- Updated `utils.args_val.validate_args` to perform additional checks.
- Added a `visualise` option in `shallow.fnn.F_NN`.
- Added code documentation in all files.
- Split the codebase into a more maintainable structure.
- Added documentation: `README`, `ROADMAP`, `RELEASE`, `CONTRIBUTING` and `EXAMPLES`.

- Added ability to modify activation functions in `shallow.fnn.F_NN`.
- Added ability to create a model using a `dict` or a `pandas.DataFrame` in `shallow.fnn.F_NN`.

- Added `shallow.fnn`: Easily create customisable feedforward neural networks with support for dynamic hidden layer configurations.
- Added `utils.gpu`: Introduced utility functions for seamless GPU setup and integration, enabling faster computation and streamlined workflows.