Some additions to make this more useful as a library
- Move testing only dependencies into dev-dependencies
- The library itself now uses surf instead of reqwest, which is more flexible over runtimes
- Add some crate features to allow configuring which backend to use
- Add logging for requests and responses
Several cleanups:
- Flesh out the README
- Make the interface a little easier to use
- Add some examples
- Add some (sparse) documentation for public components
- Mark the `FinishReason` and `Engine` enums as non-exhaustive so new members can be added in the future without breaking backwards compatibility
