Fix crash with minified functions

This is an example of a valid minified function that doesn't work with the regex in toFunction:

    function profileModelWorkerRunner(){var Moment=eval("require")("moment-timezone");self.onmessage=function(event){var profileModelClass=eval("require")(event.data.profileModelPath).default,profileModelWorker=new profileModelClass(Moment,event.data.timezone),params=event.data.params;var result=profileModelWorker.check(params);postMessage(result)}}

I've replaced that code with an eval, which is safer than parsing JS code (which is not a context-free grammar) with regular expressions.

Debug Port Range

automatic redirection of debug port of child process

Defaulting `options.cwd` to `process.cwd()`, passing `options.cwd` to `worker.js`, fixing `worker.js` by setting `global.__dirname` to `obj.cwd` on init, really fixes #10

Use SIGINT instead of SIGHUP to kill child

`kill("SIGHUP")` does not work on Windows:

Error: kill ENOSYS
    at exports._errnoException (util.js:870:11)
    at ChildProcess.kill (internal/child_process.js:374:13)
    at Worker.terminate (C:\Users\xkr47\project\node_modules\tiny-worker\lib\index.js:55:15)

SIGINT works however, and fix confirmed elsewhere also: https://github.com/balderdashy/sails/issues/846#issuecomment-25187082

Adding `require` to the inline script context for convenience, fixing API mistake by removing `close()` from the instance & updating README