Results of Jason Turner's review of the library

[hanickadot]

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His notes:

• Utilize [[nodiscard]] at least in the public facing functions
• Consider some explicit for your constructors
• Are there missing test cases eluded to by the unused functions?
• Re-evaluate older "todo" comments
• Consider making post-increment operators & qualified (thanks Bjorn)
• Maybe some more comments?
• consider moving to braced-init explicit conversions from function style casts in some places
• use = default where appropriate instead of empty function definitions
• Add test for implicit return of match to bool :smile:
• Remove inline from constexpr trivial constructors that should be = default anyhow