Some quality-of-life improvements

This is version three because it is version three of the save file format. It now saves loaded libraries into the spreadsheet save file, so that the sheet is self-contained. This is a backwards- but not forwards-compatible change. This version also adds the batch feature, so that the spreadsheet program can be used as a calculator, or a spreadsheet contents can be used in scripting.

Included libraries (from Cygwin for mingw64-x86_64; I didn't see a need for the latest changes to upstream ncurses):

• GMP : 6.3.0-1
• libstdc++ : 11.4.0-1
• ncurses : 6.4-20230812