New padding when encoding trytes to bytes
Bug #5 made it clear that the padding values had important drawbacks.
Version 1.3.0 fixes this drawback, but leaves trytes encoded in bytes in v1.2.0 incompatible with decoding in v1.3.0 or later.
The padding byte is used for any length that is not divided by 5. Thus, IOTA seeds of 81, will be affected by this fix.