Missing impl Error for JobSchedulerError

[czocher]

Adding and std::error::Error implmenentation for JobSchedulerErrror would make it much simpler to use with some error handling libraries, such as eyre.

I suggest using thiserror to auto-generate an implementation.

@mvniekerk if you find this to be a good idea I can implement it, just notify me ;).

[mvniekerk]

Hi @czocher
Check out v0.7.0, it implements std::error::Error now.