Simple loader

Hi,

I put together some stuff (which I don't think is particularly controversial) and added it as a pull request, mainly to give you a chance to look through it.

It contains:

* a benchmark
* basic http handler for haml files
* some more tests, and I changed the name of the `io` test class to `testcase` to avoid conflicts with the `io` package.

Again, I don't think there's anything controversial in this pull, so if you just leave it for a couple of days or send me a quick 'ok' I'll integrate it into master myself.