Feature: add ability for the server to serve from a list of directories

[msoulier]

It might be nice to allow the server to serve from a list of directories instead of just one. The only problem here is when someone sends a WRQ request, where do you write to? Likely the first one.

[msoulier]

The main issue here is, I think, where to put uploaded files. I think one directory should be used for incoming, and a list of directories used to serve from.