Fixes rendering of "0" values

[holic]

{{=age}} with { age: 0 } will render "0"
{{=name}} with { name: false } will render "false"
{{=name}} with { name: null } or {} will render ""

[holic]

Hmm...didn't mean to have the second commit included in this pull request. Thoughts on adding support for functions in 40c4dc0?

[jasonmoo]

Hey thanks for the contribution. I decided to take a slightly different tack. Making zero printable but keeping false and null as empty values. I think it makes a bit more sense. (6418d7e)

I think the functions are better handled by the logic generating/rendering the templates than embedded in the supplied params. This seems like another possible point of injection.