Fix broken 'levenshtein' test.
Improve performance of 'cartesianWith'.
Add syntax for lexical grouping.

Parenthetical groups can help readability by allowing
emphasis of data flow to discourage stack-based thinking.
They are typed in the same way as composition, so the
language remains purely associative.
Remove 'lint' from 'default' rules.
Add timing flag to Makefile.