Update BridgeDB's specification
We have a BridgeDB spec but it's outdated and was last modified in 2013. We should update the specification so it reflects BridgeDB's current implementation. We should also cover Moat, our new BridgeDB metrics (legacy/trac#9316 (moved)), and maybe our anti-bot mechanism (legacy/trac#31252 (moved)).
We should get the spec to a point where it can provide newcomers with a comprehensive understanding of BridgeDB's overall design.