Plus42 Equations, Preview Release

[Thomas Okken]

New update:

1. Preserving the stack during SOLVE and INTEG, so you can use REGX/REGY/REGZ/REGT and get results reflecting the initial state of the stack. (Once SOLVE and INTEG return, they'll leave results of their own, of course, so at that point, the stack will no longer be preserved.)
2. Created EQN versions of several PGM functions. The idea is to eliminate the ambiguity between "FOO" meaning a program starting with LBL "FOO" and an equation stored with STO "FOO". This distinction was already explicit in XEQ vs. EVALN, and now the same applies to PGMSLV vs. EQNSLV, PGMINT vs. EQNINT, PGMVAR (formerly PRMVAR) vs. EQNVAR, and VARMENU/VARMNU1 vs. EQNMENU/EQNMNU1.
3. If::invert() no longer generates code twice.