There is no way of retrieving the code coverage report programmaticaly

For the development of our JS Mutation testing framework [stryker](http://github.com/infosupport/stryker) we want to programmatically receive the code coverage report. We're using karma via the [public api](http://karma-runner.github.io/0.13/dev/public-api.html).

Right now: we have 2 issues:
1. We do not know when the coverage report has been written.
2. We need to collect the coverage report from disk.

I want to add a new feature: 2 birds with one stone.

I want to raise an event called `coverage_complete` whenever the reporter is done with a coverage report. In order to do that, i want to add the `emitter` as inject-able in `reporter.js`.

Next, i want to add a new reporter type: `inMemory` or something. When that reporter is active, it will provide the result of `collector.getFinalCoverage()` to the `coverage_complete` event. I don't want to add the report to every event throw, because of possible performance overhead. Only when the `inMemory` report type is in the list.

@dignifiedquire do you agree with this approach?

Start in reporter.js and trace how coverage reporters receive the collector and finish writing reports; inspect collector.getFinalCoverage() and the existing event flow. The work is done when a coverage_complete event is raised after reporting and the inMemory reporter supplies the final coverage without affecting other reporter types.

Written by the indexing model from the issue text.