discid: also display track durations in minutes and seconds

Example:
Track 1       :      150    22310 (04:57.47)
Track 2       :    22460    27737 (06:09.83)
Track 3       :    50197    30417 (06:45.56)
Track 4       :    80614    20214 (04:29.52)
Track 5       :   100828    32490 (07:13.20)
Track 6       :   133318    11394 (02:31.92)
Track 7       :   144712    20188 (04:29.17)
Move sectors to time code to its own function.

Use it for total length as well as tracks.
Use "sector" instead of "frame" to be consistent.
Merge branch 'discid_track_duration'

see pull-request #25
update AUTHORS