Powder: Create output CIF

[jl-wynen]

https://confluence.esss.lu.se/display/DAM/DREAM+-+Create+output+cif

[jl-wynen]

Introductory explanation of the format: https://gemmi.readthedocs.io/en/latest/cif.html

[jl-wynen]

There are a number of packages for handling CIF files, many outdated.

• The GEMMI project linked above is still maintained and seems useful. It is used by easyScience for reading CIF files. But it can't write files.
• Similarly, NCrystal also seems to only have a reader.
• easyDiffractionLib and EasyCrystalography have a writer. Talked to Piotr, he agrees that it in principle makes sense to extract the CIF handlers into a separate package that we could use. However, it remains to be seen how complicated it is to make that independent of the easyScience internal data structures.

Also, easyScience is currently implementing support for CIF2. I don't want to implement a writer for CIF1 at this point. So I'm moving this issue to blocked for now until we have a reader to test with.

[jl-wynen]

It doesn't look like easyScience will provide any utilities that we can use. I'm now looking into using gemmi (which ES uses internally). It does actually have a writer as well.