Automate the testing of tutorials to ensure cross-platform compatibility

see mika's comments here:

https://github.com/crate/crate-tutorials/pull/3

it's vital that our tutorials *work*. more so than the rest of our documentation, I would say -- because the tutorials are likely to be a user's first impression

we want the tutorials to work across the widest possible array of operating systems and setups

testing this manually each time is a hassle, and probably won't be done reliably. so, we should come up with a way of testing (i.e., executing) the tutorials automatically as part of the CI setup

not sure what the best approach is here. so creating this issue to collect thoughts, discussion, etc