First revision of function partials

[mikkotikkanen]

First suggestion for fixing #30

Now it's just a simple running of the function. This could be refactored to have single callback and cleaner structure. Any ideas what should be used as this for the partial function? Or what parameters it should have?

[tandrewnichols]

@mikkotikkanen I mentioned in your issue that I migrated this to https://github.com/tandrewnichols/hogan-xpress. I would like to implement this concept, as it seems like a common enough use case. Maybe you could open either an issue or a PR there for further discussion.