Short term:
- Allow more complicated conditional expressions
- STOP command

Medium term:

- LINE INPUT
- CLS?
- YETI (needs only LINE INPUT?)
- Basic_Print & Basic_Input subs for output_perl, so that when you translate
  a program into Perl, the I/O is more like BASIC's. (May be Hard, actually.)
- Upgrade test suite
- Update termbasic (NEW, LIST, etc.)
- other intrinsic functions: tab, sqr...
- upgrade error handling (Carp, etc.)
- Upgrade basic.pl & other scripts, possibly include switches (and pod!)
- Improve pod for LB & its subpackages

Long term:

- colon (multiple statements on a line)
- output BASIC, debug BASIC code
