Added

• runtime calculation procs in engine module engine.runtime. These calculate the time of a song, in frames.

Changed

• Duration type in exports/wav renamed to SongDuration, it now contains a number of loops or a time amount using Duration from std/times
• WavExporter's progress and progressMax procs are now always in units of frames.

Fixed

• Bug with arpeggio sequences treating -1, -2, etc as 255, 254, etc. The was added as an unsigned byte instead of a signed one. This caused songs with negative values in arp sequences to have the highest note play (resulting in high pitched chirping).