Fix empty attribute values
Merge pull request #155 from mmun/fix-empty-attrs

Fix empty attribute values
Bump version.
Add removeAttribute to DomHelper.

Needed by Ember to allow abstraction of `element.removeAttribute` (in
case we end up with special logic).

Also, dovetails with `dom.setAttribute`.
Merge pull request #156 from rwjblue/dom-helper-remove-attribute

Add removeAttribute to DomHelper.
Bump version.
Fix attribute hook indentation

Closes #157.
Pass number of block params to block helper
Merge pull request #158 from mmun/block-params-count

Pass number of block params to block helper
Remove dead code
Defer block params implementation to the `set` hook
Merge pull request #159 from mmun/block-params-new

Defer block params implementation to the `set` hook
Do not cache parent node as element

The element property on a morph is never cleared, however the parent of
a morph's start and end nodes may change if it is attached to a document
fragment which is appended to DOM.

Because of this, the parent cannot be cached on a morph's element
property.