Tspex

- Fixed a bug in the `entropy` function that raised a `ValueError`.

- Add support for expression matrix with `,` as thousand separators.

- Add support for Excel input files.

- TSI is now an individualized scoring metric. This change was made to reflect the original description of this metric in Julien, Philippe, et al. (2012).
- In the tutorial, genes that are not expressed in any of the five selected tissues were removed from the analysis, improving the visualization of the results.

- Corrected typos in the docstrings.
- Removed a unused variable from the `spm` function.
- Raise warnings if the input DataFrame contains non-numerical columns or if there are duplicated gene names in the index.

- Added the `sort_genes` argument to the `plot_heatmap` method.