Replace attribute selector note with class selector, class demo & class test

Replaced attribute selector [name=name] inline documentation (as referenced doesn't work in HenrikJoreteg/Happy.js#42 and HenrikJoreteg/Happy.js#52) with class selector documentation and added working example of class selector to demo.html and class input selector to test.js
No, sloppy removal of debugging remnants.  I'll update this shortly