Remove superfluous #define BOOST_PP_VARIADICS 1.
Replace when<is_valid<...>> by when_valid<...>
Add laws to Enumerable.
Add the overload utility to Functional
Work around bugs in Clang 3.5.
Experiment with adding operators to Types.
Type: add a unary operator+ turning lvalues into rvalues.

Fixes #11
Fix Doxygen warnings
Work around Clang bugs to make the String compile.
Improve unit tests for detail::create
README: Clang 3.5 is now mostly supported!