Previously, if `salt`, `iv` and/or `uuid` options were supplied as strings to
`.toV3()` they would be passed to `pbkdf2Sync`/`scrypt` as strings. That could
result in errors during encryption. Also, during decryption these options were
always converted to Buffer instances such that supplying strings during
encryption could result in output that could not be decrypted.
This commit fixes the inconsistencies, guards against bad inputs, and also
makes encrypted output match up with the output of other wallet libraries, e.g.
`ethers`, whenever the equivalent encryption options are used consistently
across libraries.
Michael Bradley, Jr
Jack Cook