Add a step1 test to make sure that implementations are properly
throwing an error on unclosed strings.
Fix 47 implementations and update the guide to note the correct
behavior.
- types: low-level mapping to the implementation language.
- core: functions on types that are exposed directly to mal.
- printer: implementation called by pr-str, str, prn, println.
- env: the environment implementation
- Also, unindent all TCO while loops so that the diff of step4 and
step5 are minimized.
