docs/gst/gstreamer-sections.txt: Add docs for new methods.

docs/gst/gstreamer-sections.txt: Add docs for new methods.

Original commit message from CVS:
* docs/gst/gstreamer-sections.txt:
Add docs for new methods.
* gst/gstevent.c: (gst_event_new_latency),
(gst_event_parse_latency):
* gst/gstevent.h:
Add new LATENCY event to configure latency in a pipeline.
API: gst_event_new_latency
API: gst_event_parse_latency
* gst/gstmessage.c: (gst_message_new_buffering),
(gst_message_new_lost_preroll), (gst_message_new_prerolled),
(gst_message_new_latency), (gst_message_parse_buffering),
(gst_message_parse_lost_preroll):
* gst/gstmessage.h:
Added messages used in draft-latency.
API: gst_message_new_lost_preroll
API: gst_message_parse_lost_preroll
API: gst_message_new_prerolled
API: gst_message_new_latency
* gst/gstquery.c: (gst_query_new_latency), (gst_query_set_latency),
(gst_query_parse_latency):
* gst/gstquery.h:
Implemented new latency query as in design doc.
API: gst_query_new_latency
API: gst_query_set_latency
API: gst_query_parse_latency