- Remove BOOST_PARSER_STANDALONE, and make that the default. The bits of
Boost that we might use are used automatically when they're available (as
discovered via __has_include).
- Remove the non-essential uses of Boost from the examples.
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.
- Update text and stl_interface files.
- Flesh out concepts constraints, using C++20 proper instead of cmcstl2.
Remove SFINAE constraints (though SFINAE may make a comback for C++17
support).
- Remove parser concept entirely. Matching parser_interface<...> should
suffice.
- Add CXX_STD to CMake files, a la text and stl_interfaces.
