Implement careting in terms of Value.Caret()
Separate "util" package.
parse.Error -> util.ContextualError
Add Evaluator.Eval; let it return ContextualError.
Move eval.envAs* to value.go.
Implement table indexing.
Fix Evaluator.pop.
Fix careting.
Improve eval error msg a bit.
parse.Tree -> Parser.
Parser.stopParse should only zero p.lex.
Put environmental variables into a special variable $e.
$!pid -> $pid.
Slight improvment of error message.