Readme shows string input not binary.

[Martin]

mcf = scrypt_mcf('Hello World')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/site-packages/pylibscrypt/hashlibscrypt.py", line 72, in scrypt_mcf
    return mcf_mod.scrypt_mcf(scrypt, password, salt, N, r, p, prefix)
  File "/usr/lib/python3.6/site-packages/pylibscrypt/mcf.py", line 216, in scrypt_mcf
    if b'\0' in password:
TypeError: 'in <string>' requires string as left operand, not bytes

Change Readme to show:

mcf = scrypt_mcf(b'Hello World')