file paths in nodeunit.options.reporter

[nheath]

The current implementation requires the reporter be referenced by name, which assumes the reporter is registered with the nodeunit that this module requires. Instead, if the reporter is unknown, assume it is a file path and require() it. This would make customizing reporters easier for use in CI processes. This seems to be a stanard approach, with examples below. Alternately, is there another preferred approach for registering a custom nodeunit reporter?

nodeunit CLI: https://github.com/caolan/nodeunit/blob/master/bin/nodeunit#L121-L126

grunt-jscs, uses config: https://github.com/jscs-dev/node-jscs/blob/master/lib/cli-config.js#L145-L161

grunt-contrib-jshint: https://github.com/gruntjs/grunt-contrib-jshint/blob/master/tasks/lib/jshint.js#L49-L60