grid_io changes

[sophie-newman]

Here the following changes have been made to grid_io and in the grid creation scripts:

• log10ages -> ages (yr) in grid creation
• metallicity -> metallicities (dimensionless) in grid creation
• The attribute log_on_read has been added to flag if an axis should be logged during interpolation
• fixed the BPASS grid creation scripts which weren't working

• Currently, changing log10ages to age will cause some issues:

• e.g. if you do fig, ax = grid.plot_specific_ionising_lum(ion='HI') with this new grid then you will get the error AttributeError: 'Grid' object has no attribute 'log10age' since this assumes log10age

After this PR, the following PRs then need to be done:

• implement the log_on_read in the interpolation stage
• alternative axes should be dealt with
• implement grid_io in the Cloudy scripts

Issue Type

• Enhancement

Checklist

• [x] I have read the [CONTRIBUTING.md]()
• [x] I have added docstrings to all methods
• [x] I have added sufficient comments to all lines
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no pep8 errors
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[WillJRoper]

Looking good so far! I'm going to make some more specific comments on the changes but one big thing: the dataset names must be plural (i.e. age -> ages, metallicity -> metallicities). This is so we can automate reading axes on the Synthesizer side.

[WillJRoper]

I want also to be able to change the axis name when log_on_read is True, e.g. age -> log10age. I'm struggling to find a nice way to incorporate this into grid_io however so any help is appreciated.

I'm not 100% sure I know what you mean here. Do you mean in the grid_axes? If so just leave that as the linear versions. We'll handle the necessary prefixes when read on the Synthesizer side.