The `hex_color!` macro currently makes an unqualified reference to the
`color_hex` crate, which users may not have in their `Cargo.toml`. This
PR re-exports `color_hex` from the root of `ecolor` and changes the
macro to use the re-exported path.
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* Closes https://github.com/emilk/egui/issues/2644
fe454573db