Removed unused "constants" variable in pelement.js

Since the PElement code that used constants.AUTO has been moved to
addons/p5.dom.js in 2c7bdd36, this is an unused variable and triggers
a JSHint warning when running the Grunt build.
Remove QUnit references from Grunt and Package.json

Since we're using Mocha and Chai to run tests now the QUnit section
in the project Gruntfile was no longer relevant. This removes the
Grunt configuration for QUnit, and removes grunt-contrib-qunit from
the project's Package.json module dependencies.
Update docs/ and lib/ with latest Grunt build
Merge pull request #224 from kadamwhite/fix-build-errors

Fix build errors