Fixed broken link for Canvas demo source code

Due to structure refactoring some of the links to source code is broken
Fixed broken links to source codes
Merge pull request #168 from sachanacar/patch-1

Fixed broken link for Canvas demo source code
Merge pull request #169 from sachanacar/master

Fixed broken links to source codes
Fixed broken GitHub link
Merge pull request #170 from samdutton/master

Fixed broken GitHub link
Added Structual SIMilarity calculation in a JS file. Used for checking
SSIM between contiguous frames in a near-frozen frames subtest of
camtest.js.