fix: remove dependencies on Buffer (#24)

[avbentem]

Fixes #24 (the EcmaScript 5 in TTN Payload Formats do not support Buffer), and gets rid of:

[DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.

[coveralls]

Coverage decreased (-0.02%) to 98.909% when pulling 17410ac on avbentem:master into 6c4d356 on thesolarnomad:master.

[avbentem]

Oh well, I guess that decreasing the lines of code also made the coverage drop by a whopping 0.02% :-)

[joscha]

Thanks!