HTTP/1.x pipelining performance testing

[vietj]

• immutable response headers
  • API
  • rendition caching
• inlining
• lazy create request inbound message queue
• more inlining
• request headers reuse connection header constant
• ChannelPromise implementation piggy backing to a Vert.x future
• event-loop strict mode
• remove HeadersMultimap dummy head node
• investigate using duplicate instead of slice in Buffer#getByteBuf()
• avoid duplicating context

[vietj]

Closing, most improvements have been done separately in master, there are a few potential improvements though like duplicated context reuse