Allow one of "XEWIDT" to refer to none, errors, warnings, info, debug
and trace, respectively because they're immediately recognizable. Well,
except maybe the X.
PIPEWIRE_DEBUG="I" is equivalent to PIPEWIRE_DEBUG="3" for example.
This is an attempt of breaking up the documentation, currently spread across
several pages. We're left with a few high-level topics with various things
grouped underneath those.
Further refinement is necessary, but this can now be done in incremental steps
over massive reworks.
