Build fails when no changes to documentation

Closes #1

See merge request !3

we use `diff-index` to test for no changes first.

Resolve "Build and publish styleguidist documentation"

Closes #1

See merge request !2

- retrieve a list of the components to document
- creates merged set of the components' dependencies
- creates a merge of the components' source from GitLab
- creates the documentation with `styleguidist`
- pushes the updated documentation to GitHub Pages