Compatibility with latest xBOUT

[johnomotani]

When the next version of xBOUT is released, the theta dimension will change to being named y in xBOUT-loaded grid files. Then we will need to update scripts/hypnotoad_plot_grid_cells.py to be compatible with that change.

• Updated doc/whats-new.md with a summary of the changes

[mikekryjak]

Where is that xBOUT change? I couldn't immediately see it on the repo. It's a welcome change but would break a lot on my end, so would be good to take a look.

[johnomotani]

Where is that xBOUT change? I couldn't immediately see it on the repo. It's a welcome change but would break a lot on my end, so would be good to take a look.

Only affects loading grid files, not normal output.
boutproject/xBOUT#307

[timothy-nunn]

@johnomotani thanks for this, can confirm that this PR + #191 + v0.3.0 of boutdata fixes #189 and allows grids (which need to be re-created with these new software versions) to be plotted using hypnotoad-plot-grid-cells.

Is it maybe a good idea to add a test to hypnotoad-plot-grid-cells in this PR? E.g. running hypnotoad.scripts.hypnotoad_plot_grid_cells:main during one of the connected_doublenull_orthogonal cases?

[johnomotani]

Is it maybe a good idea to add a test to hypnotoad-plot-grid-cells in this PR?

hypnotoad-plot-grid-cells is tested in the 'utilities' job. We seem to have got to a point where there is sometimes a long time between PRs being made/merged into this repo. It might be useful to add a regular check (e.g. once per month) of master to catch these version incompatibility issues. I'll add that into #191 and we can see if it helps.

[johnomotani]

Released a new xBOUT, so this should be ready to merge once it's updated. Maybe after #183?