refactor/149-update-to-c++-20

[jharwell]

Here are things I know I should change:

• Add usage of designated initializers for structures--way easier and clearer to
  initialize them that way than having to define regular constructors.

• inline static const std::string -> static constexpr const std::string

• Switch from boost::mpl to boost::hana, because it supersedes it, and gives
  much more intelligible error messages.

• Add more move references (&&) to functions which consume their arguments to
  make intent clearer.

• Remove NS_START(),NS_END() macros so that my code parses cleaner with doxygen.

• Refactor HAL so that all the units returned in sensors/actuators are in SI
  units, regardless of whatever nonsense ARGoS does.

• Benchmark -Os vs -O2 for large swarms to see what I should go with, or make it
  a cmake switch.

• Switch to mixing aggregate (with dots) initialization and regular constructors
  for structs, which is supported in C++20. E.g., foraging_strategy::params.

• Maybe switch to using the format strings in the C++ library for logging,
  rather than printf().

• Switch to using referenced parameters where needed in XML, so that I don't
  duplicate configuration (e.g., arena grid for both loop functions AND robots).

• Switch all uses of the decorator pattern to private inheritance where
  appropriate--way better encapsulation.

• Look into iwyu again, and the clang flag for timing builds to see where I
  could improve.

• Switch from func(void) to func(), per modern C++ (I think).

• Introduce concepts into RCPPSW to formalize some of the decls that need to be
  present in templated types for stuff to work.