Make use of the Boost.Config/Boost.Predef and cleanup macros

I will suggest to start by using the existing configuration macros

The examples I give are for Boost.Config

BOOST_FIT_NO_EXPRESSION_SFINAE - BOOST_NO_SFINAE_EXPR
BOOST_FIT_HAS_TEMPLATE_ALIAS - BOOST_NO_CXX11_TEMPLATE_ALIASES
BOOST_FIT_HAS_RELAXED_CONSTEXPR - BOOST_NO_CXX14_CONSTEXPR

There are others that don't exists yet (or I don't understand them to do the mapping :( ), and that could be proposed in the future if needed by two libraries (not now). Anyway a description of what the macro is detecting would be welcome.

BOOST_FIT_NO_ORDERED_BRACE_INIT
BOOST_FIT_NO_UNIQUE_STATIC_LAMBDA_FUNCTION_ADDR
BOOST_FIT_NO_TYPE_PACK_EXPANSION_IN_TEMPLATE
BOOST_FIT_NO_STD_DEFAULT_CONSTRUCTIBLE
BOOST_FIT_NO_UNIQUE_STATIC_VAR

BOOST_FIT_HAS_MANUAL_DEDUCTION
BOOST_FIT_HAS_MANGLE_OVERLOAD
BOOST_FIT_HAS_COMPLETE_DECLTYPE

The following macros seems to need a clean up as they are defined explicitly
# define BOOST_FIT_NO_CONSTEXPR_VOID 1
# define BOOST_FIT_HAS_STATIC_LAMBDA 1

The following are not used
BOOST_FIT_HAS_RVALUE_THIS