o_random is not disposed in ElGamalEncryptor class

[bazzilic]

o_random in ElGamalEncryptor is IDisposable and therefore should be disposed. I suggest adding Dispose method to ElGamalEncryptor and making it IDisposable, and do a using (...) {...} in ElGamalManaged.EncryptData (and everywhere else ElGamalEncryptor is used too, if any).

Also, see CA1001 and CA2213

@cheeyixu please fix!

[bazzilic]

Resolved by #6