Maintain preset flags

Previously this was just bashing over any flags you passed in.
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
patch DOMTokenList instead of using a wrapper
remove predeclaration of property and move comment to top
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 #85 from jakemac53/DOMTokenList

patch DOMTokenList instead of using a wrapper
Merge pull request #58 from jakemac53/master

Maintain preset flags
Make an import without an href properly generate an error event.
fix(base.js): HTMLImportsLoaded event dispatch throws error on IE

When using a  script loader such as require.js or system.js the HTMLImports polyfill will not load correctly on all versions of IE. It will throw a JavaScript error causing the program to crash. This is caused by the use of `CustomEvent` to dispatch the HTMLImportsLoaded event, which results in `Object doesn't support this function`. By explicitly using the older `createEvent` technique, the bug is fixed.
fix(HTMLImports): use initCustomEvent for HTMLImportsLoaded

This commit switches the api to use initCustomEvent. It also cleans up some quotation inconsistencies.