Implement map based properties per issue #41.

Regarding:
https://github.com/lviggiano/owner/issues/41

Implemented a first version of map based properties. This version supports Map\<String, String> currently. Implementing different value types might be much more interesting, considering you might get type conversion errors per-entry.

Sample properties:

	map1.value1=abc
	map1.value2=def

Sample class:
	
	interface MyConfig extends Config {
		@MapValue("map1")
		Map<String, String> map1();
	}