adding pitch bend support

[motifn]

Adding pitch bend support. In order to compile, I had to alter the midi-file declaration file too.

Notes:

1. The pitch bend value is passed through with no translation. Perhaps you want to perform some translation, and/or doc-comment on legal range of values.
2. Obviously the version of the package needs to be updated

[tambien]

@motifn looking through the code. everything is looking good. Is it possible to include a validation test or two to verify the behavior of the new feature? Glancing through the midi i've got on hand, i don't see any that have pitchBend, so can't easily verify this PR.

[motifn]

I emailed you a midi file with pitch bends if that helps (the github interface doesn't let me choose a midi file attachment). The file has pitch bends of both up and down, up to two semitones, assuming that the pitch bend range is 2 semitones, so demonstrates the maximum possible range.

Also, I think it would really good to scale the pitch with value: Math.floor(pb.value * 8191.5) as mentioned in the comment here:

#80 (comment)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[tambien]

thanks for the PR! sorry took a while to find time to merge it. should be published soon