This add `sway-ipc.7.scd` that documents the IPC protocol.
This also increased the minimum scdoc version from 1.8.1 to 1.9.0 to
allow for table cells to be continued on the following line
These are not yet implemented, and will be exposed as a configuration command
rather than env variables when implemented.
This also adds a reference to sway-input(5) in xkb env configuration. Maybe we
should just un-document these instead.
