Merge pull request #50 from tindzk/master

WindowTimers: More concrete signature for setTimeout()
Merge pull request #52 from tindzk/master

Improve MouseEvent
Element: Fix setAttribute()

According to [^dom] all parameters are required. Currently, it is
possible to skip the arguments without an error being issued during
compilation.

[^dom]: http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-F68F082