instrument now returns information about lines conditions and functions.

Hello Fabio!

I am opening this small pull request to make it possible to callers of the `instrument` function to access information about lines, conditions and functions available in a file, which is not possible currently (or only by parsing or executing the instrumented file, which I want to avoid).

This is needed for the following change in attester: attester/attester#77

Do you think you could integrate this change in node-coverage, and publish a new revision in npm?