Basic: Reduce GOSUB use. Partial self-host to step3

Basic: Reduce GOSUB use. Partial self-host to step3

step4 runs out of space attempting to load the program. Step2 and
step3 run out of memory (stack exhaustion) for more complicated forms.

- Use GOTO with return label on our stack instead of GOSUB for:
    - APPLY function in types.in.bas
    - "apply", "map" and "swap!" core functions
- Implement DO TCO. Change EVAL_AST to detect if we are called from DO
  and exit one element early.
- Remove GOSUB recursion from EQUAL_Q
- Inline PAIR_Q. Reduce REPLACE stack use.
- Remove one level of GOSUB/stack by calling REP with GOTO
- Simplify mal/step2_eval.mal to remove use of (or ) macro in
  eval_ast.
- Fix ON GOTO/GOSUB line detection in basicpp