Switching to new jshint and standards. Adding istanbul for coverage.

Example refactor based on this: https://github.com/Strider-CD/strider/issues/308#issuecomment-30253366

I've also dropped the Makefile, which I totally understand if you don't agree. At clock are pretty aligned with this view http://substack.net/task_automation_with_npm_run

There was no code coverage so I've added our standard istanbul setup. Again if that is too much let me know:

https://github.com/serby/strider-runner-core/blob/master/package.json#L9

It does highlight that coverage is low on this module, which I'm happy to address if we can agree some thresholds:

     Statements   : 42.05% ( 82/195 )
     Branches     : 29.59% ( 29/98 )
     Functions    : 41.46% ( 17/41 )
     Lines        : 44.02% ( 81/184 )