Lambda support

[jabley]

I did it in https://github.com/jabley/mustache/commits/master if you wanted to steal.

[cbroglie]

Thanks @jabley! I don't have time to work on that myself, but will gladly accept a PR if you or anyone else wanted to remake those changes here. I'll leave this open for future reference.

[flowchartsman]

There's an existing PR for this: #28. If we could get a review of it, I would be pleased to address any issues to get this support in. Would be really useful for framework-defined convenience transformations for user-driven content.

[timonmasberg]

+1 would be wonderful if we could get this merged @cbroglie

[cbroglie]

I merged #67 (a version of #28), it adds partial support for lambdas

[hgl]

@cbroglie it seems 1.3.0 actually doesn't include #67.

[cbroglie]

I've just released v1.3.1 with those changes