This swaps github.com/kivikakk/golex for github.com/cznic/golex.
The old lexer would have taken 3.5 years to load a set of 5000 test rules
(quadratic time complexity for input length), whereas this one takes only 32ms.
Furthermore, since the new lexer is embedded differently, this gets rid of the
global parser variables and makes the rule loader fully reentrant without a
lock.
This also removes the now obsolete scalar count() function and corrects the
expressions test naming (broken in
2202cd71c9 (L6R59))
so that the expression tests will actually run.