Implement C++0x tuples

This library implements a fixed-size collection of values with a variable number of heterogenous types. The specification for this library is contained in Chapter 20.3 [tuple] of the C++ draft standard and consists of the following sections:

20.3 Tuples [tuple]
20.3.1 Class template tuple [tuple.tuple]
20.3.1.1 Tuple traits [tuple.traits]
20.3.1.2 Construction [tuple.cnstr]
20.3.1.3 Tuple creation functions [tuple.creation]
20.3.1.4 Tuple helper classes [tuple.helper]
20.3.1.5 Element access [tuple.elem]
20.3.1.6 Relational operators [tuple.rel]