Add more matchers

[follesoe]

Currently we only have toBe, toEqual and toBeNil. We should probably add more matchers such as:

• toHaveSlot to check if a object has a given slot
• toContain to check if a List/Map contains an object
• toBeTrue and toBeFalse to check boolean expressions
• toThrow to check or exceptions

Adding the toThrow will greatly simplify our own testing of matchers, so it would make sense to implement this one first.

[follesoe]

The toThrow matcher can be extended to take an expected parameter.

• If the parameter is nil, then simply check if an exception is thrown (current implementation)
• If the parameter is a Sequence, check that an exception is thrown, and that the error message matches.
• If the parameter is a Exception object, check that the exception thrown is of same type, and same message as the expected exception.