Generate opacity files

[isaacgsmith]

In the bottom of docs/stardis.bib, in the "Opacity Data" section, there are several papers that contain data for cross-sections, gaunt factors, or hydrogenic bf/ff departure coefficients. The papers are also in the TARDIS Zotero in the STARDIS/Stellar Opacity Data subfolder. A few guidelines for the cross-section files (as the readers for the others haven't been built yet, see #42):

• No column or row headers.
• # is for comments.
• If there is no temperature dependence, wavelength is the first column and cross-section is the second column.
• If there is temperature dependence, wavelength is the first column and temperature is the first row. Leave the top left entry blank, though. The cross-sections then are filled in according to their wavelength and temperature.
• The reader does flat extrapolation beyond the min/max wavelength/temperature, so if you want the opacity to be zero beyond a certain wavelength/temperature, you need to include that in the table.
• Wavelengths must be in Angstrom, temperatures in Kelvin, and cross-sections in the appropriate CGS units.

However, see #61 as these guidelines may change.

We will want these in the refdata repo (either tardis/refdata or a new stardis/refdata) eventually.