Add a way to view the executed notebooks

[eteq]

Right now the CI doesn't leave any build artifacts, so it's impossible to use the CI to build the generated notebook. It would be better to have the CI-generated executed notebooks be visible to reviewers. This is possible, but requires $ (specifically, an Amazon S3 bucket) to do using travis. Circle CI does this pretty trivially and for free. Should consider switching to Circle CI on this basis...

cc @arfon

[arfon]

I think it's OK to write to an S3 bucket. Want me to set one up?

[eteq]

An update here: it turns out Travis won't leave artifacts for PR builds (I learned by trying to get it to work...). Which is really annoying and means Travis probably can't be used to do this without a bunch of custom scripts. So getting this to work may require switching to CircleCI or some other similar service that is better about artifacts.

[pllim]

If you are okay with access limitations, Jenkins CI can upload artifacts as well. We have been using it at DATB/SCSB to auto upload candidate new truths from nightly test runs.