Merge pull request #15 from ahdinosaur/master

implement and test getElementsByClassName for multiple class names
2.11.0
implement DOMElement.prototype.getElementsByClassName
cleanup document at end of each test
test DOMElement.getElementsByClassName
cleanup in new test
Merge pull request #16 from Raynos/DOMElement.getElementsByClassName

DOMElement.prototype.getElementsByClassName
2.12.0
update docs to include getElementsByClassName as per https://github.com/Raynos/min-document/pull/16#issuecomment-52416800