Prop 324: Updates for Negotiation and Simulation Testing

Changes:

• Rework exit negotiation logic a bit
• Specify using ntorv3 with extension fields for negotiation
• Clients only request congestion control; exits and services control sendme_inc
• Rework onion service negotiation for descriptor-controlled FlowCtrl protover and sendme_inc value
• Add bounds checks on sendme_inc for clients
• Update parameter values based on Shadow results
• Improvements to TOR_VEGAS algorithm based on simulation testing
• Additional consensus parameters for RTT N-EWMA smoothing and TOR_VEGAS queue use caps
• Clarify N_EWMA smoothing, and relocate it to its own sub-section.
• TOR_VEGAS now defaults to CWND/RTT BDP estimator
• Minor TOR_VEGAS alg bugfixes
• Add a 'delta' parameter to TOR_VEGAS for steady-state backoff
• Consensus param update notes and param range fixes.
• Add glossary of common congestion control acronyms
• Misc clarifications

requested review from @dgoulet

assigned to @dgoulet

mentioned in merge request !59 (closed)

mentioned in merge request tor!535 (merged)

merged