Feature/sprkstep

[balos1]

Todo:

• Merge add sprkstep examples sundials-codes/answers#16 first
• Update example output in repo with output from Jenkins

Rendered docs can be viewed here: https://sundials.readthedocs.io/en/feature-sprkstep/index.html

[drreynolds]

I've reviewed everything except src/arkode/arkode_sprkstep.c. I'll look at that tomorrow.

[drreynolds]

Overall this looks great. I tried to give "suggestions" for all easily-fixable items to streamline the update process.

[drreynolds]

This is looking really great. I have only a few more items to resolve before I think this is ready.

[gardner48]

This looks good, I think all that's needed is to update the answer files for the GitHub CI and once those are merged update the submodule commit here.