Provide coercing methods for the jailed configuration: getintXXX(), getboolXXX(), getfloatXXX() and friends. This is done be refactoring Configuration and putting the coercing methods into a common mixin.

{"__comment1": "Comment 1",
 "key1": "the value",
 "key2": 2,
 "key3": 5.7,
 "key4": true,
 "key5": false,
 "key6": 255,
 "__comment2": "Comment no 2",
 "key7": "Umlaute: ÄÖÜäöüß"
}