Semver-major changes

GlkApi:
- Don't accept Arrays
- Don't export Const
- Export RefBox, RefStruct, etc from the module, not Glk itself
- Remove dom_prefix option?
- Hide internal properties of classes (ex, `str` in `WindowBase`)? (Maybe not necessary, as it only affects JS terps. For a TS terp only the interfaces are exported, so these properties won't be accessible.)