[Tagging] "by_appointment"

[Richard Weait]

The taginfo seem to be silent on how to tag a shop or service that is
only open by appointment.  A discussion on the wiki has some
interesting points.

http://wiki.openstreetmap.org/wiki/Talk:Key:opening_hours#Museum_opens_only_on_request

opening_hours=by_appointment seems logical but collides with
conventional opening_hours.

Perhaps

opening_hours:by_appointment=*

using the same format as opening_hours, so that a location that is
open weekdays, and by appointment evenings and weekends might be
tagged as

opening_hours=Mo-Fr 09:00-17:00
opening_hours:by_appointment=Mo-Fr 18:30-22:00 Sa-Su 10:00-13:00

We've not used any indication that an appointment is required for tags
like amenity=doctors.  Can we just leave that be as it seems to have
been presumed opening_hours:by_appointment=yes