FYI: Edge MathML support

I'm sure this is not a surprise to many of you, but Edge is picking up the
MathML Core work of Igalia. As with Chrome (in the regular and nightly
builds), you can turn it on by enabling the Experimental Web Platform
features. The regular builds are maybe 1 -3 months behind the nightly
builds and won't show off the current state of what is in the code base.

To turn MathML on:
chrome://flags/#enable-experimental-web-platform-features
edge://flags/#enable-experimental-web-platform-features

This test page
<https://mdn.mozillademos.org/en-US/docs/Mozilla/MathML_Project/MathML_Torture_Test$samples/MathML_Torture_Test?revision=1506691>
will show off the current state. You need to pick a math font that is on
your machine. The Stix fonts are good and can be downloaded from here
<https://github.com/stipub/stixfonts/tree/master/OTF> if you don't already
have them.