Added a protected decrypt(byte[] bytes, SecretKey key) to mirror the
protected encrypt method which takes a byte array.
Exception message tweak.
Added a test for attempting to decrypt data which is too short to
contain an initialisation vector.
Added a constructor that takes a SecretKey directly as the wrapping key
and deprecated the constructor and accessors for working with a
String representation of the wrapping key.
Version increase to 0.7.0 to note the interface change in KeyWrapper.