This is a large refactor of the config parsing structure, attempting to
reduce the size of the file a bit by splitting it up into different
modules with more specific purposes.
This also fixes#2279.
This switches our own `copypasta` crate with the more standardized
`clipboard` library, which allows us to get rid of the `xclip`
dependency on X11.
Additionally, this lays the foundation for native Wayland clipboard
support once the clipboard crate is updated (or a fork is created).
Fixes#5.
