{{t}} helper uses registerBoundHelper

 * use `registerBoundHelper` to register `{{t}}`
 * `{{t}}` no longer supports passing a `tagName`
 * drop support for `I18N_TRANSLATE_HELPER_SPAN` and remove
   corresponding `taglessTranslateHelperSpec.js`
 * tests use `fooBinding="bar"` instead of `foo=bar`, per behavior
   of `registerBoundHelper`
 * mark compatibility with all Ember 1.x
 * remove vestigial `warn`, `isBinding`, `uniqueElementId`,
   and `TranslationView`
Merge pull request #165 from jamesarosen/james/rbh

{{t}} helper uses registerBoundHelper
Ember.Handlebars.get -> Ember.get

Now that we're using `Ember.Handlebars.registerBoundHelper` to construct
the `{{t}}` helper, we don't need to use `Ember.Handlebars.get`. It's
deprecated and does unnecessary work.
Ember-I18n 3.x supports Ember 1.x

 * relax Bower dependency on Ember to `^1.0`
 * resume testing against Ember canary
 * current Ember canary (what will be 1.9) relies on
   Handlebars 2.x
Merge pull request #166 from jamesarosen/james/resume-canary

Ember-I18n 3.x supports Ember 1.x