Initial release.

Features:

• REPL mode and script execution
• recursive descent parser
• INTEGER, CONS, SYMBOL, FUNCTION, T, NULL types
• reference counting for all objects except T and NIL
• single namespace for variables and functions (Scheme-like)
• basic arithmetic, boolean, list and I/O functions, IF, COND, LET, LET*
• DEFUN and LAMBDA with environment capture
• function return value caching with automatic side effect detection