Demo at https://github.com/swcarpentry/lesson-example/pull/132/.

1.  Created `bin/repo_check.py`.
2.  Moved `require()` to `util.py`.
3.  Updated `Makefile` with new target.

1.  Splitting commands to clean intermediate R files into separate target.  These files must be committed to the repo, so they shouldn't be deleted under normal circumstances.
2.  Modifying intermediate file generation to create fig/rmd-* rather than fig/swc-rmd-*, since this template is used by other carpentries (not just SWC).

1.  Renaming Ruby file to use underscore in name (consistent with other `bin` scripts).
2.  Generating `_includes/all_figures.html` for the first time when creating a new lesson.