support OEP-8

[NashMiao]

Is your feature request related to a problem? Please describe.

OEP-8, a cryptographic item standard, which has been accepted as standard. Therefore, Python SDK should provide a collection of interface for other developers to use.

Describe the solution you'd like

1. deploying a test contract in test net.
2. add interface to call OEP-8 contract.
3. publish a 2.1.x PyPi package.