Use the standard API instead of the legacy API to search for Issues, Repos and Users

We should use the standard API instead of the legacy API:

- The Legacy API will eventually be removed
- In at least one case the legacy API does not work correctly: it only returns open issues even when setting the state to 'closed'

The standard API allows us to add a new value to the state param in the 'find issues' function: if we set this parameter to 'all' it will return both 'open' and 'closed' issues

The format returned by the standard API and the legacy API is different, so this change may be BC-breaking

I would be grateful if you could bump up the tag value if you accept this PR as we need to use it in a dependent project