Add `@Factory` to enable static factory methods as alternate to constructors

[dblevins]

Factory methods must be public static.

        @Factory
        public static Address makeone(@Param("street") @Nullable final String street,
                                      @Param("city") @Nullable final String city,
                                      @Param("state") @Nullable final State state,
                                      @Param("zipcode") @Nullable final int zipcode,
                                      @Param("country") @Default("USA") final String country) {
            return new Address(street, city, state, zipcode, country);
        }