Improve JFixtureJUnitRunner

[richkeenan]

It'd be very nice to have the JFixtureJUnitRunner class override the invocation of test methods so they can inject specimen instances as method parameters.

@Test
public void example_test(String orderId) {
   sut.setId(orderId);
   ...
}

• This behaviour can only be done through the Runner, not the Rule.
• Should you have to annotate the method or parameters with @Fixture? It's technically not required, but the explicitness might be nice