Drop namespace::clean

Should be okay with Moo's "everything before `use Moo::Role` is not a method"
behavior.

	modified:   dist.ini
	modified:   lib/MooX/Role/Pluggable.pm
Fix '_default' dispatch to plugins; missing event name in arg list

Also POD cleanups and fixes. Could still use work.
Minor test tweak
v0.120004

  Fix '_default' dispatch to plugins; event name was missing from args.

  POD cleanups/clarifications. Could still use work.