Make README acceptable to twine

Drop support for Pysparse and Python 2.7.

Switch to pyproject.toml.

Harmonize solvers. Last version that supports Py27 and Pysparse.

This maintenance release:

- Addresses compatibility with recent releases of
  Python 3.12, NumPy 2.0, SciPy 1.14, and PETSc 3.20.
- Adds `conda-lock <https://github.com/conda/conda-lock>`_ environment
  lock files with specified compatible versions of FiPy prerequisistes.
- Fixes numerous documentation errors.

Add logging and fix compatilibity with PETSc and NumPy

Maintenance release

sub-sub-tag for CHANGELOG edits

Don't do this again!

This release fixes assorted viewer issues, fixes a problem with conve…

…ction

boundary conditions, and introduces spherical meshes.

Make compatible with numpy 1.18

Deprecated `order="FORTRAN"` has now been removed.

Other changes found during release of FiPy 3.4

Add support for PETSc