Add 'interact.js' and 'drag and drop' keywords
Add snap actions array to docs

Closes #33
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Add snap actions array to docs
  Add 'interact.js' and 'drag and drop' keywords
Trigger dropactivate and dropdeactivate events
Improve dropzone demo to show more scenarios

Setup dropzones with different accept options.
Highlight draggable if it can be dropped.
Add a draggable that can't be dropped.