Began making cell utils cleaner.
Began renewed push to finish draft of `NTorFSM`.
Began making cell utils cleaner.
Merge branch 'cleaner_cell_utils' into ntorfsm

Conflicts:
	oppy/cell/util.py
Fixed style/bugs in immutable cell representations.

Also implemented `RelayBeginCell` as an immutable.
Cleaned up `NetInfoCell`;

Also fixed-length cells now have `payload_len=None`.
Did some cleanup in `NTorHandshake`.

Also did some cleanup in `RelayExtended2Cell`.
Did some cleanup in `Created2Cell`.
Replaced `except Exception` with more specific one.
Fixed import renaming oversights.
Merge branch 'cleaner_cell_utils' into ntorfsm

Conflicts:
	oppy/circuit/handshake/ntorfsm.py
Finished drafting `NTorHandshake`.
Added better error reporting in `OnionCircuit`.
Squashing bugs in `crypto` and `NTorFSM`.
Trying to send `RelayExtend2Cell`.
added missing methods to encryptedrelaycell
Made `manager.py` test use a cached consensus file.
Now caching server descriptors for debugging.
Started using `signing_key_to_sha1()` helper func.
Fixed alignment in `updateRelayCellWithDigest()`.