Handles I-frames-only `segments`, providing a basis for the creation of trick-play functionality.

**parse-stream.js**

- add match statement for parsing the `EXT-X-I-FRAMES-ONLY` tag
- add test case

**parser.js**

- add a property `iFramesOnly` to the `manifest`
- add a function to validate the minimum version required
- trigger a `warn` event if the minimum version required is not supported or undefined, as required by the specification
- add test case

https://datatracker.ietf.org/doc/html/rfc8216#section-4.3.3.6

- update `README.md` documentation