Remove dependence on underscore

[crertel]

Would you be interested in a pull request that removes the dependency on underscore?

We only use:

• _.defaults
• _.isFunction
• _.isString

[Troy Goode]

@crertel Yes, I'd be open to that.

[crertel]

Great. I'll send one in when I get a chance.

[Noor Alhiraki]

I found underscore.js dependency trivial, so I removed it and bumped the version here:
noor@f9a024e

[crertel]

Thank you! I'm sorry I didn't get to it--was swamped at work. :(

[Noor Alhiraki]

No worries :)

We all are... aren't we?!

[Troy Goode]

published to npm as 2.1.0