Refactor proxy

[mostafa]

The proxy has a few issues that need to be addressed before it can be further enhanced:

v0.8.x milestone:

• Remove elastic mode #359
• Refactor server and proxy #343 (enable bidirectional communication)
• Make Proxy.PassThrough async #33 (async communication)

v0.9.x milestone:

• Investigate other proxy mechanisms #425
• Routing #399
  • Implement signal, action and policy system #422
  • Enable multi-pool client connections #398
  • Add connection multiplexing to avoid 1:1 mapping of client to server connections #55

Future milestones

• Expand load balancing strategies #593

Related

• Feature parity with proxies #206