update project to be a long-lived fork of grunt-contrib-jshint

The upstream maintainers of grunt-contrib-jshint decided they didn't
want to support inline jsx conversion, so convert this project into a
standalone fork suitable for publishing to npm.

In addition to adding the support for converting jsx files that was
originally proposed in https://github.com/gruntjs/grunt-contrib-jshint/pull/163,
this PR also updates the package metadata to reflect this forked
repository and sets the name of the package to grunt-contrib-jshint-jsx.