Renamed Container template tuple_type to element_type
* Container can theoretically be specialized on types other than Tuple template specializations
** this is now reflected in the typedef naming scheme
** writeup of requirements for types to be used by Container and Iterator should be written down
* the std::tuple specialization typedef provided by the Tuple template was renamed to value_type
** e.g. the internal _relative_ representation of types is named element_type and the constant value types are named value_type
* Modified test cases accordingly