v0.12.2: HTTP Upgrades

Bug Fixes

• http2:
  • implement graceful_shutdown for HTTP2 server connections (b7a0c2d5, closes #1550)
  • send trailers if Payload includes them (3affe2a0)
• lib: return an error instead of panic if execute fails (482a5f58, closes #1566)
• server:
  • fix debug assert failure when kept-alive connections see a parse error (396fe80e)
  • correctly handle CONNECT requests (d7ab0166)

Features

• body:
  • make Body know about incoming Content-Length (a0a0fcdd, closes #1545)
  • add Sender::abort (a096799c)
• client: add set_scheme, set_host, and set_port for Destination (27db8b00, closes #1564)
• error: add Error::cause2 and Error::into_cause (bc5e22f5, closes #1542)
• http1: Add higher-level HTTP upgrade support to Client and Server (#1563) (fea29b29, closes #1395)
• http2:
  • implement flow control for h2 bodies (1c3fbfd6, closes #1548)
  • Add content_length() value to incoming h2 Body (9a28268b, closes #1546)
  • set Content-Length header on outgoing messages (386fc0d7, closes #1547)
  • Strip connection headers before sending (f20afba5)