Release v3.1.0

This is a major release. Main changes:

• The calc_shape method of the stereology module has been renamed to two_step.
• A new method, called calc_volume_fraction, has been added to the stereology module. It uses the lognormal parameters estimated by the two-step method to estimate a volume fraction occupied by any range of grain sizes.
• Several templates with different examples of grain size population analysis have been added. These include:
  • quantification of grain size distributions (grain_size_analysis_template.ipynb)
  • approximation of grain size distributions using stereological methods (stereology_analysis_template.ipynb),
  • paleopiezometry (paleopizometry_template.ipynb).
• Restructuring of the script organisation and refactoring code to improve readability.
• The script documentation has been completely rewritten for the new script organisation. It should now be easier for newcomers. See new documentation at https://github.com/marcoalopez/GrainSizeTools/wiki