Instrument JavaScript files and collect coverage.

- No exclude list, all JS files are instrumented.
- Remove collection of YUI Code Coverage data.
- Display of coverage data is broken because it expects YUI data.
Add coverage summary. Instrumenting now works.
Add `--no-instrument` option.

Useful when you've already instrumented code with Istanbul.

Use with the `--coverage` option.

For YUI, we plan to use `--no-instrument --query 'filter=coverage'`
to only collect coverage data for files loaded with that filter.
Apply coverageOptions if `--coverage` is set.

YUI will normally use `--coverage --no-instrument
--query 'filter=coverage'` options instead of `--coverage` by itself.

When `--coverage` is used, check for the coverageOptions config
object and apply those settings if found.

This allows for YUI to set defaults for coverage in its .yeti.json,
allowing developers to run `yeti --coverage` instead of a longer
command.
Add `--coverage-report` related options.

- Defaults to summary, but can be set to any Istanbul report option,
  such as lcov, html, json, etc.
- `--coverage-dir` is where coverage reporter are written. Defaults to
  ./coverage.
Fix lint errors.