changed empty, now it uses destroy to clean every children tree
this change need a check on destroy, because childNodes returns
textNodes
on dispose i removed the _fireEvent reference breaking the circular
reference and allowing the gc to clean up the memory (tested with
sIEve-0.0.8)
set('html',...) don't leak but set('text',...) does, so added a
Element.Properties.text setter and done empty() before setting the text

I setup a test page that creates 1000 divs, added these divs to the
body and then use empty(), set('html', ...) and set('text', ...) to get
rid of them, causing a 1000 element leak,
with these changes I managed to drop the leaks from 1000 to 0.

This reverts commit 4c68d39.

This reverts commit 14f5deb.

revert dispose, destroy now filter nodeType, so Element.properties.text
can use empty without throwing errors, delete properties in clean.