libweston: add weston_debug API and implementation

weston_debug is both a libweston API for relaying debugging messages,
and the compositor-debug wayland protocol implementation for accessing those
debug messages from a Wayland client.

weston_debug_compositor_{create,destroy}() are private API, hence not
exported.

Signed-off-by: Pekka Paalanen <pq@iki.fi>

append the debug scope name along with the timestamp in
weston_debug_scope_timestamp API

Signed-off-by: Maniraj Devadoss <Maniraj.Devadoss@in.bosch.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

Add explicit advertisement of debug scope names.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Emre Ucan <eucan@de.adit-jv.com>