Config methods with multiple @Keys and @DefaultValues

[lviggiano]

At the moment, the @Key annotation only accept one value (as well the @DefaultValue annotation), it would be nice if for a single property we can specify multiple @Keys and multiple @DefaultValues.

Example

interface MyConfig extends Config {
    @Key({"db.driver", "db.url", "db.user", "db.password"})
    @DefaultValue({"org.h2.Driver", "jdbc:h2:~/.myapp/data", "scott", "tiger"})
    ConnectionPool connectionPool()
}

public class ConnectionPool {
    ConnectionPool(String driverClassName, String url, String user, String pwd) { ... }
    // or... better (see issue #44)  
    ConnectionPool(Class driver, String url, String user, String pwd) { ... }

    Connection getConnection() { ... }
}