Put `codepoints` and `characters` behind feature flags

[SabrinaJewson]

In the interests of reducing binary since, and since codepoints and characters contain the same information (at least I believe they should?), would it be possible to feature-flag their inclusion?

[p-jackson]

Thanks for the comment, yes that does fit into the purpose of this package.
This package aims to simply provide an authoritative list of entities without any logic, but it totally makes sense that a user of the data would need just the code points and not the characters (or vice versa).