Study stf by @jfalcou and let lest benefit from it.

Ideas:

• Use auto test case registration only.
• Use default suite, but still allow for user to specify one, e.g. for testing lest itself.
• Add ULP comparison
• Add PASS/FAIL/TYPE_IS/EXPR_IS/EXPR_TYPE
• Add typed tests (see what can be done w/o Boost).
• Fail empty test cases
• Simplify reporting mechanism
• ...