Updated Assets and Claimable Balances.

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[X] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
[X] I have read the CONTRIBUTING document.
[X] My code follows the code style of this project.
[X] My change requires a change to the documentation.
[X] I have updated the documentation accordingly.
[X] I have added tests to cover my changes.
[X] All new and existing tests passed.