improve dragging by shifting the piece under the cursor
Merge branch 'master' of bitbucket.org:ornicar/chessground

* 'master' of bitbucket.org:ornicar/chessground:
  Add an example page for mobile devices
production build is working!
mobile.html and mobile-dev.html
mention production build in the readme
remove ring dependency
use node http-server for serving files
Merge remote-tracking branch 'origin/master' into touchevents

Conflicts:
	src/chessground/drag.cljs