libtracker-extract: Updated documentation example for tracker_extract_get_metadata()
libtracker-extract: Updated documentation example for tracker_extract_get_metadata()

Also updated the Since: and added information about what changed since
0.10 for people upgrading

hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker