Pass the shell's environment on to child processes
Re-work the command invocation mechanism in the evaluator.  Command-lines are better supported, both in spirit and in actuality (more characters are allowed including paths etc.).  Many cleanups and improvements to all things: shell, lexer, parser, evaluator.  Rename some items in the lexer.  Add the "Value" rule and corresponding parser to the Parser framework.
Trim whitespace around commands.  Allow absolute-paths to find programs.