update backburner

included updated documentation for the run loop as well
DRY up container tests.
[FEATURE ember-metal-computed-empty-array]

Make `Em.computed.empty` respect arrays automatically, without users having to
know to use `array.[]`.
Lazily setup observers for attributeBindings without defined values
Define HTML5 fields on input fields.

Previously, binding to this many attributes unnecessarily added a
significant performance penalty. Now these bindings are setup lazily for
values that were not previously defined on the instance.
Remove controlID inclusion from mustache
Add automated testing for prod/min builds.
Merge pull request #4269 from marcioj/old_control_helper_stuff

Remove controlID inclusion from mustache
Merge pull request #4270 from rjackson/test-minified-builds

Add automated testing for prod/min builds.
Merge pull request #4257 from rjackson/lazily-bound-attributeBindings

Lazily bound attribute bindings
Merge pull request #4237 from rjackson/dry-container-tests

DRY up container tests.
Merge pull request #4219 from hjdivad/make-empty-less-confusing

[FEATURE ember-metal-computed-empty-array]
Merge pull request #4120 from kingpin2k/update_backburner

update backburner and Ember Metal documentation