Resolve Clippy's `too_many_arguments` lint on
`handle_selection_request` by removing the `success` and `refuse`
parameters and returning a bool indicating which needs to be run.
Use the helper functions defined last commit to simplify
`incr_copy_from_x11`
Reduce the `match` statement checking if the target is the TARGET
atom to an if statement. Although using `match` statements as
`if`/`else if`/`else` chains occur elsewhere, this one is both only 2
cases, and already of particular relevance to the current work.
Refactor `paste_impl` to be much easier to read. I did this code algebra
way back while investigating #142, but since I never figured that out,
the change has just been sitting in my stash.
refactor: simplify paste_data logic, some unnests
cc011f3251