Wrap getComputedStyle

Fixes #64
Implement event constructors for Safari and IE

This implements event constructors for

Event
CustomEvent
UIEvent
MouseEvent
FocusEvent

More can easily be added as needed.

Fixes #58
Merge pull request #86 from arv/event-constructors

Implement event constructors for Safari and IE
Update README.md
Merge pull request #84 from arv/get-computed-style

Wrap getComputedStyle
Merge branch 'master' of github.com:toolkitchen/ShadowDOM into html-body-head-element