Implemented `relaydatacell.py`.
Began work to wrap/unwrap user data.
Attempted to make `GET` request with `DummyStream`.
Merge branch 'master' into relay_data
Began adding proper digest-updating support.

See issue #63.
make some quick bugfixes
got relay_data back
fix cipher order
Fixing bugs to get relay data cells working.
Made relay data work!
Cleaned up some debug cruft.
Drafted `RelayEndCell` implementation.
Made `RelayEndCell.__repr__()` easier on the eye.
Added nicer support for `RELAY_END` handling.
Made `shared.net_status` be a mockup.

Download up-to-date netstatus docs with `tests/cache_netstatus_docs`.
Fixed socks request's `dest_addr` representation.
Mission Accomplished!
Merge branch 'relay_data'

Oppy is now able to relay user data between a browser and a remote
resource!