Track dependencies

[ForbesLindesay]

It would be really useful if ejs offered a way to get a list of the dependencies for a file when compiling it. This would enable recompiling only when some files have changed. Ideally this would work roughly the same as jade's support for this feature.

[TimothyGu]

Adding it to .compile() is simple, but there doesn't seem to be a better way to do the same thing for .render() without changing the API or boxing the string (which gives terrible console.log output without .toString()).

[TimothyGu]

See WIP: https://github.com/mde/ejs/tree/deps

[ForbesLindesay]

I don't need it on .render, so that would be fine with me. I think it would be fair enough to say that people who need access to the dependencies must use the compile api.

[TimothyGu]

@mde, any comments on this?

[mde]

Doesn't seem all that useful for render anyhow. I can see the utility for this though, and it doesn't add much complexity to the code. Let's do it.