Fix "canvas not defined" when using click callback.

Derived the relevant canvas for the click callback from evt.target.
Merge pull request #21 from stephenr85/patch-1

Fix "canvas not defined" when using click callback.
Remove extra jQuery call in src
Use different Bootstrap CDN source
Save the image data as text instead of data URL, fixes #4
Save all reference images
Fix drawMask
Save mode
Use IndexedDB instead of localStorage (see Gecko bug 995910)
Remove remote web font dependency
Allow skipping w/o ref image
Print data URL if there is no reference image
grunt and shell script for tests and compare
Print data url if the test fails
jshint fixes
Enable Travis-CI; compare in pull requests, test in branches
Update README
Fix pull request check
Merge pull request #28 from timdream/pr-test

Fix pull request check
Update API.md

Adding click and hover HTML5 canvas notice.