Add Lodash compatibility

[andfaulkner]

Given what typecast is using underscore for, there's no real reason it couldn't also allow you to use lodash - e.g. by letting you pass in whichever _ library you prefer rather than having a hardcoded require or define call to underscore in the factory along with some conditionals in the code based on whether _ is lodash or underscore.

It's not exactly a trivial task, but it'd be very valuable for adoption and usability. Indeed, the lack of lodash support is the only reason I'm not using Typecast.

...or you could switch to lodash :). (I partially jest, but IMHO it's a much better library at this point).