Jasmine 2.0

These changes port the Jasmine matchers to Jasmine 2.0, which is an incompatible API change.

At the same time imagediff's own test suite is ported to Jasmine 2.0 to be able to test those changes.

I've refactored a few tests that were difficult to port and added a file `spec/IntegrationSpecRunner.html` to see the `toImageDiffEqual` matcher in action. This can be used as an integrative test. I've moved the unit tests away from integrating with the Jasmine infrastructure directly, following the style of the Matcher specs in Jasmine's own test suite. The way the tests have been written for Jasmine 1.x seems incompatible with Jasmine 2.0. In addition Jasmine is now available over npm, so I've added the dependency to package.json. The jasmine-node runner port to Jasmine 2.0 is still in beta, but hopefully moves into a stable version in the following weeks.