MathML: added Modernizr.mathml test
MathML: added test to check if polyfill should load

The `complete` handler cleans up the Modernizr.mathml test elements.
This handler should be removed once the bug has been fixed in Modernizr.
MathML: added JEP polyfill and working examples
Merge pull request #3821 from patheard/mathml

MathML polyfill