Add Rspec save_fixture helper for generating jasmine html fixtures.

The goal of this change is to support automatically generating HTML fixtures for Jasmine tests when you run your Rspec view tests.

This is a *huge* benefit for projects that use the [jasmine-jquery](https://github.com/velesin/jasmine-jquery) library to avoid HTML fixtures from getting out of date with the actual generated source.

Example of wiring Rspec + JasmineRails:
https://gist.github.com/wireframe/e73ce5eed16ce3e01e28