General refactors.

[HexDecimal]

Making a list of various changes to make this code more up-to-date. Most of these are easy on their own. It will just take time to do them all. I've already finished most of these kinds of changes to Umbra.

• TCODList should be replaced with std::vector in all cases.
• Remove new/delete from libtcod types. These can be treated as values without major issues. Any exceptions can use smart pointers instead of new.
• Pointer types should express ownership, ideally with std::unique_ptr, but also std::shared_ptr if necessary. Non-owning pointers would still be raw of course.
• Class attributes should be initialized. Just put {}; at the end of simple types rather than = nullptr; or = 0;. Any defaults should be moved from the class constructor code to the class itself.
• Pointers to strings should be replaced with std::string in many cases. Mostly in non-contexpr cases such as class attributes or local variables. In some cases null strings should be replaced with empty strings. Always replace strdup.
• #define X Y constants should generally be replaced with static constexpr auto X{Y};/static constexpr auto X = Y; constants.
• #define macros should all be replaced with constexpr functions.
• Low level calls such as memcpy and strcmp should generally be replaced with high level operations.
• C-style arrays like int foo[2] should be replaced with std::array<int, 2> foo{}, etc.
• File operations should use C++17 <filesystem>.
• For-loops over containers should prefer ranged-based loops. for (auto& x : y);
• Many class methods are missing const, noexecpt, and [[nodiscard]] qualifiers.
• Empty constructors and destructors should use = default;, they should not have an empty function in the source.
• Small functions with few or no dependencies should be moved inline.
• Functions which take pointers, but don't handle nullptr, should be changed to take references.
• Macros such as MIN or CLAMP should be replaced by their C++ functions.
• Virtual class overrides are missing the override qualifier.
• String formatting functions should use fmt.
• Temporary local variables which don't change should be qualified with const.
• Unions should be replaced with std::variant.

In general follow the C++ Core Guidelines.