Added support for recursively fetch external data

[Thumbleweed]

When using panini in a medium-sized project, i noticed it was not possible for fetching .json data in nested subfolders. I thought this was weird, since it is possible for partials to be nested in a folder structure.

I changed the selector for fetching data, so it does it recursively. I also changed the unit test for loading external json data, so the json file is in a subfolder.

[thomasmattheussen]

I have also fixed a caching problem with the data files.

When "requiring" files in node, the responses are cached, and thus panini.refresh doesn't actually refresh those files. I fixed this by deleting the require.cache entry for the file you want to load.

[gakimball]

Merged, thanks!