Update dependencies to use lodash instead of underscore.

I'm going to be using this for my own needs, but I thought you might be interested in updating to lodash from underscore, as lodash is evolving (evolved?) to becoming the standard. Just so it didn't break anything, I made the dependency on the underscore'd version of lodash, but I imagine a switch to the mainline lodash would not be difficult.

Like I say, I did this purely for selfish reasons, but if you want it, you're more than welcome.