Plus42 Equations, Preview Release

[Thomas Okken]

New update:

1. PATH variable. You can create a list named PATH, stored in the root directory, to provide a search path for programs and variables. You store directory references in PATH (see here). The directories referenced by PATH are searched after the current directory and its ancestors.
2. Command completion menus now show variables and programs from ancestor directories and PATH. Items from the current directory are shown in white text on black buttons, as usual; items from ancestor directories and PATH are shown in black on white. For operations that modify their operands, only the contents of the current directory are shown.

Many, many changes in the code. Use with caution; back up your state files!