Rfactor

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- Small updates to documentation
- Improved warning/errors
- Added lightweight compute_diagnostics`` that computes diagnostics for input
rainfall timeseries, see 1f0a7f5.
- Fix pandas warnings:
- Use pandas assign to create new columns.
- Use pandas concat instead of pandas append.

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- Cleaned up data-files avaible in repo.
- Included test for ``maximum_intensity_matlab_clone`` function and updated
tests.

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- Matlab code is translated to Python.
- Two major bugs in the Matlab code are fixed.
- Added Matlab code legacy.

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New version that avoids the need to define an independent file providing the
links to all input data files needed to analyse the R-factor.

Previous functionalities are preserved, and work in the same way:

- Compute the erosivity and R-factor values based on rainfall input data.
- Analyse the computed erosivity and R-factor values (for Flanders).

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- Implemented R-factor Python processing functions.
- Implemented Python wrapper for KULeuven `compute R-factor` Matlab script.
- Implemented use of Octave to run Matlab scripts.
- Set-up package.
- Added examples and test data.
- Added test