Convert lexer and formatter tests to test generators, so that one failure does not prevent running the others.
Convert lexer and formatter tests to test generators, so that one failure does not prevent running the others.

spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments,spencerlyon2/pygments