Feature Request: Extensible/Customizable Value Escaping

[Zulu-Inuoe]

I recently had the need to generate a URL from a mustache template. Because in these cases the values must be url-encoded rather than HTML escaped, it would have been very helpful to have conntrol over the mustache::escape function.
While there's other workarounds for this, I think a worthwhile feature would be for mustache to expose some mechanism for controlling the escaping performed on template renderings.

I think a reasonable implementation could be to define a mustache:*escape-function* variable which callers to mustache:render could bind. And/or, an additional optional or keyword parameter to mustache:render to achieve similar.

I'm happy to implement but I'd like some feedback/thoughts.

Thanks!

[kanru]

I merged #26 which adds *escape-tokens* so you can turn it on or off. It would be nice if you can customize the escape function too!