the tests to get them building when Hana is not used; disable building the
examples when Boost.Hana is not in use, so that they can keep using the much
nicer hana::tuple::operator[] instead of parser::get().
This completes the changes to make Hana optional.
constants like llong; provide a tuple accessor get(); use these throughout the
code.
Also, adapt the code in detail/hl.hpp to work with hana::tuple and std::tuple.