Replace scipy obsolete interp2D. Add scripts for massive directory comparison and plotting.

• remove most raw binary file I/O, retain ability to convert .dat to .h5
• add magtools.py
• make str2func more robust and modern
• improve finding of supporting executables e.g. gemini.bin
• fix longstanding bugs in unused code for equilibrium_state
• fix plotting bugs

• Python >= 3.7 required

The workarounds for Python < 3.8 can make confusion.

expand_envvar works like Fortran/MatGemini now--can expand any text between @...@ environment variable

numerous bugfixes for new grid implementation, including making write work like matlab.

add more coord conversion methods

no more 2D axes swaps with new grid system

large number of improvements, removal of dead code, etc.

• bugfix netcdf grid write
• add .zst archive extraction
• add user function injection like MatGemini
• refactor plots/ into several files for clarity