Is That A Glimmer In Your Eye?

Includes a fix for compatibility with Glimmer2. Note that at least one compatibility issue remains, see #66

Closed issues:

• [Glimmer] Doesn't work in canary since glimmer was enabled #64
• Explicitly define compatibility with Ember 1.13+ #62
• Allow users to handle "failed to render into" errors #58

Merged pull requests:

• Use getDOM util to get dom reference in glimmer2 #65 (bantic)
• [DOC] Add Ember version compatibility to README #63 (lukemelia)
• Use native doc.getElementById when available #61 (bantic)
• Test ember-alpha in CI. #60 (rwjblue)