Shopify/batman — pull request #416 by nciagra (2012-05-03 21:40:38+00:00)
Title: Make event and observable API's slightly more consistent with onFirst and observeFirst.

Previously, there was no way to have a single use observer, and the name `once` was misleading as it could work for either single use events or single use observers. This makes the API for both available and explicit.

Open to suggestions on the naming.