Updated logging capabilities

[JDBetteridge]

Fixes #394

[tommbendall]

Thanks for doing this Jack, I think it's really helpful to have this pulled out from configuration.py

[JDBetteridge]

There's more to come, I think I can get KSP residuals to be logged. I think what we need is a custom KSP monitor, like I have written here (but much simpler), which logs the exact same information that is output by ksp_monitor_true_residual to the Python logger and then turn off the PETSc internal logger to avoid duplication.

[JDBetteridge]

I think this is ready for another review 🙂

Resolved (stale review)

[tommbendall]

This is really good. I can confirm that I have run an example in serial and in parallel on my machine and that the log files appear in the results directory for that example.

Thanks very much!