docs/libs/gstreamer-libs-sections.txt: Add new methods to docs.

docs/libs/gstreamer-libs-sections.txt: Add new methods to docs.

Original commit message from CVS:
* docs/libs/gstreamer-libs-sections.txt:
Add new methods to docs.
* libs/gst/base/gstbasesink.c: (gst_base_sink_class_init),
(gst_base_sink_init), (gst_base_sink_set_ts_offset),
(gst_base_sink_get_ts_offset), (gst_base_sink_set_property),
(gst_base_sink_get_property), (gst_base_sink_wait_clock):
* libs/gst/base/gstbasesink.h:
Add ts-offset property to fine-tune the synchronisation.
API: GstBaseSink::ts-offset property
API: gst_base_sink_set_ts_offset()
API: gst_base_sink_get_ts_offset()