Set SCHEME to mit and add simple book.mit target.
Updates to get book.mit loaded without errors.

Fix up macros to use R5RS define-syntax where possible. Add a custom
define-macro to enable define-meroonet-macro.
More fixes for book.mit.

Make DISPLAY-EXCEPTION call WRITE-CONDITION-REPORT to get more
information about conditions that are signalled.

Add defintions for WHEN, UNLESS, and LIST*.

Return a thunk from the MAKE-TOPLEVEL arg to INTERPRETER and SUITE-TEST,
rather than calling BIND-CONDITION-HANDLER, which was dropping into the
REPL before the RESUME continuation could be SET!.
Replace TOP-LEVEL-ENVIRONMENT with USER-INITIAL-ENVIRONMENT.
Pass mandatory environment arg to EVAL when SCHEME=book.mit
Add format.scm and pp.scm.
Set SHELL explicitly for mit-scheme's run-shell-command.
Define SYSTEM proc for book.mit.
Don't use uppercase letters in gensym6f.

Mit-scheme's string->symbol will wrap the symbol name in pipe chars if
the string contains uppercase letters. Symbols that contain pipe chars
are not valid C identifiers, so just pass lowercase strings to gensym6f.
Clarify variable names in define-macro expansion.
Fix indentation of define-macro.
Redefine mit-scheme's eval to make the environment argument optional.