Add the ! postfix operator and !! expression.
Also add the ++ string concatenation operator.
Also allow specification of standard input in the test scheme.
Resolves#7, #18.
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #25
Co-Authored-By: Glen Whitney <glen@nobody@nowhere.net>
Co-Committed-By: Glen Whitney <glen@nobody@nowhere.net>
