Release v2.3.0

[joelvdavies]

Once #82 has been merged, v2.3.0 can be released by following the steps on https://github.com/muon-spectroscopy-computational-project/Developer-notes/blob/main/package-maintenance.md

Other notes:

• The issue #81 will not automatically close when #82 is merged so it should be closed manually (or otherwise 'closes #81' should be added to a PR merging the v2.3.0 branch into main)

Release notes

• Added 'results_function' parameter for improving fitting capabilities and included least-squares as a fitting_method #77 by @joelvdavies in https://github.com/muon-spectroscopy-computational-project/muspinsim/pull/78
• Some sparse matrix usage improvements by @joelvdavies in https://github.com/muon-spectroscopy-computational-project/muspinsim/pull/79
• Removed a limit on a maximum of 4 fitting_variables #77 by @joelvdavies in https://github.com/muon-spectroscopy-computational-project/muspinsim/pull/78
• Fixed an issue preventing fitting of ALC experiments (or any with a magnetic field as the x_axis parameter)
• Fixed an issue preventing fitting from running with mpirun #77 by @joelvdavies in https://github.com/muon-spectroscopy-computational-project/muspinsim/pull/78

Full Changelog: https://github.com/muon-spectroscopy-computational-project/muspinsim/compare/v2.2.1...v2.3.0