c mode everything in ch 12
Fix up symbol-table: no more default values for idx. Errors on new
entries which helps keep function counts correct.
Also fixed type vs scope on idx in env-add.
Chapter 11 shenanigans.

Added shebang to make jack directly executable.
Added syntax-class definitions for call and var to fix up ambiguities in compile-term.
Fixed and unified env compilation for function args and locals.
Fixed blank returns by adding a static 'push constant 0'.
Improved error messages so I know what to work on next.
Implemented calls in compile-term. Finally.
Fixed up command-line handling using command-line macro instead of current-command-line-arguments.