Adds libltc

Linear (or Longitudinal) Timecode (LTC) is an encoding of timecode data
as a Manchester-Biphase encoded audio signal. The audio signal is
commonly recorded on a VTR track or other storage media.

libltc provides functionality to encode and decode LTC from/to timecode,
including SMPTE date support.

libltc is the successor of libltcsmpte.

Homepage: http://x42.github.io/libltc/