Write "how to be nice to the Tor network" spec

In talking to Jake, I realized that there are still some people who expect jtor to be a workable Tor client one day. In fact, we've even been writing some funding proposals that make this assumption.

One of the main issues we're going to have with an alternate Tor client is that while it may follow our network specs, it will have different observable behavior than the mainline Tor client.

First, this different behavior will make users partitionable. Fine, we can accept that. But we should finish writing path-spec.txt so authors of other clients can have at least a chance of doing things the way "real" Tor does.

Second, it's easy to make client-side decisions that harm the Tor network. For examples, you can hold your TLS connections open too long, or do too many TLS connections, or make circuits too often, or ask the directory authorities for everything. We need to write up a spec to clarify how well-behaving Tor clients should do things. Maybe that means we write up some principles along the way, or maybe we just identify every design point that matters and say what to do for each of them.