gst/subparse/gstsubparse.*: Add 'encoding' property (#341681).

gst/subparse/gstsubparse.*: Add 'encoding' property (#341681).

Original commit message from CVS:
Patch by: Young-Ho Cha  <ganadist chollian net>
* gst/subparse/gstsubparse.c: (gst_sub_parse_dispose),
(gst_sub_parse_class_init), (gst_sub_parse_init),
(gst_sub_parse_set_property), (gst_sub_parse_get_property),
(convert_encoding):
* gst/subparse/gstsubparse.h:
Add 'encoding' property (#341681).
* gst/subparse/samiparse.c: (characters_sami):
Output is pango markup, so we need to escape text
between tags (#342143).