decodeFrom is no longer destructive with it's inputs.
Added isOnCurve().
Added validate().
Fixed formatting.
Factored out new functions serializeSig and parseSig.
The BigInteger class we're using supports negative integers and
encodes them with a sign bit. Since in our application we are dealing
with unsigned integers only, we need to disable this functionality by
creating two wrapper functions toByteArrayUnsigned and
fromByteArrayUnsigned.
