Remove usage of lodash from lib code

[trygve-lie]

Fixes #12

This uses the same core-util-is module as used in helmetjs/hsts#1 for checking types. When not supporting pre node.js 0.12.x versions any more, this module can be removed and one can only rely on the native util in node.js / iojs.

There was one usage of lodash .map function which now are replaced with plain higher order Array functions.

Then, there was a lodash deep copy of objects. From what I could see this copy function only copy the config object which is pretty flat and holds only String and Array values. I replaced this with a very simple shallow copy function instead. This shallow copy function only copy one level and only handle Arrays as special values. If a deep copy is wanted we could replace this with:

var newObject = JSON.parse(JSON.stringify(originalObject));

Lodash are still present as a devDependency since its used in the tests.