support reading "jshintConfig" from package.json as an alternative for .jshintrc

> If you’re working on an NPM package you don’t need to have a .jshintrc file anymore. Just put your JSHint options into your package.json file as a property named jshintConfig and you’re all set! The format is exactly the same as .jshintrc.

Related links:
http://jshint.com/blog/2013-08-02/npm/
https://raw.github.com/jshint/jshint/master/package.json
https://github.com/jshint/jshint/commit/a2a9d53a9cd4a4342375e45e2c2e3a1a3cb160cb