.ractive and .ract extensions

Hi,
any reason to have only `.html` as default extension?

In my case, i can not use API cause serving through `browserify-middleware` and have to use `.ractive` extension cause using Sails.

So a way would be to have more default extensions and another is to define them in `package.json`

First one looks simpler cause you do not need to find/read base `package.json`