feat(refactor): simplified mixin calls to use data attributes
feat(refactor): simplified mixin calls to use data attributes

Removed the 'markdown' flag because the `data-markdown` attribute
is already a flag.

jlengstorf/happy-people-do-it-better,jlengstorf/reveal.js-jade,schaab/react-unit-testing-slides,jlengstorf/happy-people-do-it-better,jlengstorf/reveal.js-jade,schaab/react-unit-testing-slides