Accept a full .jshintrc configuration file

I'd like to be able to provide a complete JSHint configuration file for the JSHint run. There are a few options that require an integer setting (such as 'maxcomplexity', 'maxlen', etc.).

The proposed solution does not heed the 'withDefaults' options. Would it be better to heed that setting with a jshintrc file as well?

I would add the necessary documentation for README as well in case you deem this pull request acceptable.