Update examples ERC-20 and ERC-721

[TucksonDev]

Description

This PR updates the Erc-20 example, to make it compatible with the latest SDK version, and adds a new ERC-721 example.

Checklist

• [X] I have documented these changes where necessary.
• [X] I have read the DCO and ensured that these changes comply.
• [x] I assign this work under its open source licensing.