brkClass Directive

Adding the brkClass ( brk-class=“className” ) directive for adding over
and down class variants.

Originally to allow same-specificity hover selectors, but also allows
more useful ‘--down’ class, rather than ‘:active’.

Added a few styles to the html to show off brkClass.
Also moved the html file out of build, as it isn’t part of the build
process, so it could get lost if the build folder was deleted.