adds instrumentation functionality using istanbul.

- this will be used to create coverage stats.
refactors instrumentation to be more efficient and adds better unit tests.
ensures that executable is unset for instrumentation.
same as before, but better!
adds coverage to gitignore.
pushing bits.
adjusts results to improve loading attributes from json.
adds coverage configuration and adjusts formatters to have a nicer getter.
adds support for coverage configuration to env and cli.
adds coverage logging to console reporter.
adds integration suite to teabag configuration (makes it easier to comment in/out).
fixes command line option for coverage reports.
updates the file that's tracked by instrumentation.
automatically turns on coverage if reporters are passed in the cli.
moves some line feeds around.
adds coverage output to base reporter.
adjusts line feeds some more.
adjusts specs to be pending when istanbul isn't installed.
updates readme.