TODO

* decode into an existing buffer, to avoid
  constantly reallocating memory
* add num traits to color types
* make this crate `no_std`
    + use [this crate](https://lib.rs/crates/embedded-io) for I/O
* split `feim` into different sub-crates
    * e.g. `feim-serialization`, `feim-colors`, `feim-images`, etc
* add bitmap images?
    + use [this crate](https://docs.rs/bitmaps)
    + or [this crate](https://github.com/heliaxdev/index-set)
* make error in decode and encode an associate type,
  not io::Error
* implement mozjpeg backend?
* generic image impl, with enum containing all enabled formats
    + create feature flag for it
    + or hide it under `enable-all-formats` feature flag?