Minor fixes to license file.

Validator should fail when FIXME present

Add validator target to makefile

Update validator to work with revised LICENSE.md.

1.  Remove copyright information about code of conduct (which isn't in this repo).
2.  Change ownership of trademark to NumFOCUS.
3.  Use uniform link syntax.

Removing FIXME from instructors.md

First should come the common workflow tasks, then commands for internal/debugging use.

Our authors use this label to mark unfinished/work in progress lessons.

Sync gh-pages with newest core changes

Fix validation of motivation.md

Revert changes when validating glossary

Skip mailto links in link validation

Removing unused files. Thanks @gvwilson, it looks good.

Merging CSS from styles repository

Merge branch 'update-template-no-css' of github.com:fmichonneau/lesson-template into update-template-no-css

add missing bracket

Upgrade bootstrap

Add validation for callout boxes

Implement template-specific callout rules. Add tests and fix bugs revealed.

Narrow def of callout: block must have heading.

Simplify way that callout counts are tracked, improve log messages, and add further unit tests of callout validation.

Ensure that callout validation is actually run

Conflicts:
	css/swc-bootstrap.css
	css/swc.css

add new line after list

this PR replaces #145 which also included the changes to the CSS.