Added features, formatting, and bug fixes :)
- Simultaneous plotting of multiple smiles columns (pull request 1) can now be done by passing in a list of smiles columns into `smiles_col` (see `examples/multiple_smiles_columns.ipynb` for a tutorial).
- Adjusting of hover box transparency (issue 3) can now be controlled with `alpha` and `mol_alpha` arguments (see entry in `examples/simple_usage_and_formatting.ipynb` for example usage).
- Usage examples split into multiple notebooks and organised in `examples` folder.
- Fixed bug (issue 6) resulting from specifying both `color_col` and `marker_col`.