Implement @Autowired for constructors.

[misha]

Common use case for a DI container. Rather than annotating fields, a single constructor would carry the annotation, and all of its arguments would be injected during construction for an @Autowired field of that type. This is an alternative to directly annotating fields that often allows for less type-fu when unit testing, as well as the ability to turn off Iroh altogether and just pass in the correct instances manually.

public class Example {

    @Component
    public static class Dependency { ... }

    @Autowired
    public Example(Dependency a) {
        Assert.assertNotNull(a);
    }

    @Test
    public void testAutowiredConstructor() { ... }
}

[misha]

This issue is tabled until I get a better sense of the direction Iroh should be heading towards (more features vs. simpler features).