0.8.0-rc1 release candidate

A release candidate for version 0.8.0.

Major new features:

• Override the default WebGL filters (#1003)
• Initial raycast functionality (#1021)
• Multiple layers of a given type (DOM/Canvas/WebGL) are possible, and they can respond to viewport movement in different ways
• Static UI layers are now possible
• A new "Controls" system that makes it easier to wire up inputs to your entities.

Here's the full release notes, and preview documentation is available. (Though you can also see the docs locally with grunt view-api.)