Add codemeta file for software preservation

[tmorrell]

Thanks for your submission to CaltechDATA! You can also preserve this GitHub
repository using the automated integration in CaltechDATA. This PR includes a
codemeta file, which lets you control the metadata that shows up
CaltechDATA. Please check that the codemeta.json file is accurate. You can set up software preservation using CaltechDATA following these steps:

1. Log into data.caltech.edu with your Caltech (access.caltech) account credentials.
2. Select GitHub from the profile menu in the upper right hand side of the screen.
3. Enter your GitHub credentials
4. Select this GitHub repository (You might have to refresh the page for the buttons to activate).
5. Make a new release in GitHub.

The DOI image I added to your README will show up once your code is preserved.

Let me know if you have any questions,

Tom Morrell
Research Data Specialist, Caltech Library