Fix `make lesson-check` warnings and add to CI workflow

[alexdewar]

This PR fixes/suppresses all make lesson-check warnings and adds it as a step in our CI workflow.

It doesn't give quite as many helpful warnings as I was hoping for, but I still think there's some value in using it (and in any case I've done it now :upside_down_face:).

Commit summary:

• Rename episode files according to Carpentries style
• Add a few missing include links.md bits to episodes
• Suppress some other warnings, including the check whether code block types are valid (we're getting a false positive here, so I commented it out -- see: 9d4e1c027adea46b3cbe558982afcbe18aed9f01)

There is a newer version of the Carpentries template that we could move to which may add some more checks and/or fix the false positive we're getting, but in any case we're going to move to the new Workbench tool at some point (#66) so it's probably not worth it.

Closes #72.

[alexdewar]

Oops -- getting a CI error. Converting to draft till I fix

[alexdewar]

Sorted. I think this is good to go now.