- HeaderName is either 32 or less inlined bytes or heap-allocated vec for more than that.
- Equality and hashing is case-insensitive
- A HeaderMap is a hashmap from HeaderName to Strings that can be
indexed with &str, case insensitive. Insertion order is also preserved
Merge ui crate with root crate.
In preparation for uploading `meli` as a separate crate on crates.io.
Workspace crates will need to be published as well and having a separate
`ui` crate and binary perhaps doesn't make sense anymore.
