[WIP] Add unlink/rmdir. Fixes #7

[mikebryant]

Here's an initial implementation of unlink/rmdir.
Seems to work locally (I've tested deleting namespaces, individual pods, and all pods in a namespace), but I haven't started writing tests etc yet.

rm -rf ends up being very slow, as it ends up populating the cache of everything underneath it, and it starts going a big wonky when it tries to delete nodes etc..
rmdir is nice and quick, and works as expected

[bspaans]

Nice one! Unfortunately I don't have time this week to do a proper review, but will pick it up early next week. Thanks!