Throw useful error message for unmatched or void element end tag.
Merge pull request #227 from oneeman/error-for-unmatched-end-tag

Throw useful error message for unmatched end tag
Fix exiting namespace when it's the last child (#223), clean up surrounding code
Merge pull request #228 from oneeman/fix-exiting-namespace

Fix exiting namespace when it's the last child (#223)
attribute morph
Add attrmoph creation to templates
setContent instead of update
Introduce setProp
In template output, use setProp instead of setAttribute
Port attr sanitization from Ember to HTMLBars
Drop destroy hook until required
Drop hasOwnProperty check for props
Fix a test for safari