Add async support for eth.contract and contract function calls

[AngeloCa]

What was wrong?

Support for async eth.contract and async contract calls would be useful

How can it be fixed?

Asyncify eth.contracts and contact calls.

[fselmo]

closed by #2484

[IlluvatarEru]

@AngeloCa How can I check in which version was this change released?

[fselmo]

@AngeloCa How can I check in which version was this change released?

You can find this information in the release notes. In this case, this was added into the v6 beta.3 release.