- inherit a predefined set of system environment variables
(the current set of inherited variables is: ahci; acpi; no_apic);
- auto-adjust the default menu option when lines are auto-removed;
- add variable substitution support for /etc/boot.cfg.local;
- make default menu options in boot.cfg.local relative to itself,
allowing one to set the default to a menu option from this file.
- add "edit" menu option, to edit menu commands before executing them;
- add "menu" boot command, to return to the menu from the prompt;
- provide more line editing features when getting input;
- fix a few potential buffer overflows as a side effect.
