Support non-clostache partials

[JulianBirch]

I'll happily write this and send a pull request. At the moment, my plan is to

1. allow you to specify a string as a partial, in which case it is interpreted as a clostache template
2. allow you to specify a function, in which case it is invoked and assumed to return HTML.

My principal reason for wanting to do this is to handle small nasty pieces of code where hiccup is a better fit, but you could use it to mix and match template engines as well.

[JulianBirch]

Looking at the code, this is hard. Doesn't mean it isn't worth doing, but it's hard to achieve directly.

[fhd]

I don't fully understand this, partials are already passed as strings. Could you give an example of what you mean?

[JulianBirch]

Actually, part 1 is "support existing functionality", part 2 is new. So you could send in a partials like this.

    { :x "Standard Clostache Partial"
      :y partial-thats-actually-a-function }

Applying this to the current code base is hard, though. But if I ever do decide to try to code compilable templates, I think it would be worth trying to separate out expression evaluation and partial evaluation.

[fhd]

Yeah, that'd make sense.

[fhd]

Then again, wouldn't a lambda do?