libzvbi-teletextdec: use AVBPrint for whitespace cleanup

Signed-off-by: Marton Balint <cus@passwd.hu>
ass: factor out ff_ass_bprint_dialog

Signed-off-by: Marton Balint <cus@passwd.hu>
ass: fix error handling in ff_ass_add_subrect

Signed-off-by: Marton Balint <cus@passwd.hu>
ass: move text_event_to_ass from textdec.c to ass.c and export it

Signed-off-by: Marton Balint <cus@passwd.hu>
libzvbi-teletextdec: output ass subtitles instead of plain text

Signed-off-by: Marton Balint <cus@passwd.hu>
libzvbi-teletextdec: dont ignore memory allocation error silently

Signed-off-by: Marton Balint <cus@passwd.hu>
libzvbi-teletextdec: propagate errors generated in page handler

Signed-off-by: Marton Balint <cus@passwd.hu>