v3.0.0

Changelog:

• The usage of all macros is now properly documented in the README
• dstruct will only use a single argument for "multi-unit" members (e.g. bytes 3) and pad any space not covered by it; this makes them more useful
• Designated initialization (.YBox=42) is now case-sensitive, as is RGBDS with symbol names
• extends lets you "include" a struct inside of another one (by @eievui5)
• Struct fields can be aliased, providing UNION-like functionality (by @eievui5)
• The separator between the "root" and member name in dstruct can now be customized
• Struct constants can now be exported by default
• Using dstructs with the wrong number of arguments will yield an error
• More internal consistency error-checking
• Performance has been improved somewhat (thanks for the help @Rangi42!)
• The examples are now tested, so they are guaranteed to compile (at least with the latest RGBDS as of this release)