v3.0.0

Release notes:

- Switch to the latest Clipboard API spec, using the `ClipboardItem` type.
- Add a `text` build to save code size for most people.
- Add an `overwrite-globals` build that can be used for polyfilling global objects.
- Fix a bug that prevented copying `text/html` in Safari.
- Fix `types` field in `package.json` to point at the full library types.
- Avoid potential infinite recursion/bugs if the caller tries to overwrite `navigator.clipboard` and/or `window.ClipboardItem`. #127