Improvements

• glz::custom now supports lambda functions along with previously supported member pointers, member functions, and std::functions.
• glz::manage has a new API: glz::manage<&T::x, &T::read_x, &T::write_x>

The glz::manage read and write functions can also be lambda functions. And, the functions registered no longer take in a glz::manage_state.
These changes make glz::manage far more flexible.

• Added DEBUG assertions to more easily catch buffer writing errors that should be impossible to occur.

Fixes

• Fixed circular includes for quoted.hpp and manage.hpp (Thanks @justend29)