#8 Add cryptographic chain of trust to protocol

[Travis Brown]

The usefulness of a filesystem to share stems from the ability to control who can write where. To this end a cryptographic chain of trust and write permisions needs to be added.

This will require public key encryption, confirming the hash based upon these keys at every node to prevent poisoning and some system to manage the keys.

Publicly writeable files will have no key or perhaps the key in the file descriptor.