Initial augment of UA sniffs to detect IE Edge mode
Make HTMLImports polyfill more robust when assigning baseURI property

This came up within the context of Cordova apps (https://github.com/MobileChromeApps/mobile-chrome-apps/issues/450)

On iOS, doc.baseURI is null, and the assignment throws a `TypeError`:

    TypeError: Attempted to assign to readonly property.

I actually don't see when it wouldn't be null since this is a new document. On Chrome, it doesn't throw, but the assignment also doesn't stick.

Instead of calling the setter, this PR creates a new property on the object itself.
Fixes a wrong test for HTMLContentElement
Merge pull request #82 from mysticatea/fixes-a-wrong-test

Fixes a wrong test for HTMLContentElement
Merge pull request #77 from agrieve/patch-1

Make HTMLImports polyfill more robust when assigning baseURI property
Merge branch 'master' into issue51
IE >11 has the CustomEvent constructor (#51)
Merge pull request #87 from jacobrossi/issue51

Fixes #51 - Trident UA sniffing issues with "Edge" mode IE on Windows 10
Fix accidental global variable.
Fix accidental global variable
Merge pull request #124 from timoxley/patch-1

Fix accidental global variable.
Merge pull request #125 from timoxley/patch-2

Fix accidental global variable
Merge pull request #1 from webcomponents/master

update