write function to reconstruct an approximate audio track from a raw SG file

[jbrzusto]

Allowing users to listen to data files post hoc might help in cases of missing or malfunctioning tags, or reveal problems with the tag finder.

[jbrzusto]

pretty obvious algorithm: paint each pulse additively into a time-domain ring buffer, taking into account the possibility of small time inversions before exporting a prefix of the buffer as completed audio.

• could combine all antennas into a single track, or one antenna per track
• use signal strength and offset frequency, but ignore noise value
• use a windowing function to reduce noise at pulse edges