add max_stable_version for crate responses

[beckend]

This is useful when creating outdated checks.

[beckend]

I have no idea what the tests are that are failing, some help would be appreciated.

[theduke]

Thanks, and sorry for the delay!

I included your commit in #56 .

The error was due to max_stable_version being an optional field. I also improved the error reporting for JSON decode errors in above PR, so debugging this stuff should be easier in the future.

[theduke]

Included in #56 .

[beckend]

Thanks!