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.

# -*- coding: utf-8 -*-

__comment1 = u"Comment 1"
key1 = u"the value"
key2 = 2
key3 = 5.7
key4 = True
key5 = False
key6 = 0o377
__comment2 = u"Comment no 2"
key7 = u"Umlaute: ÄÖÜäöüß"