release v1.1.0

[avsm]

• Add an "expert mode" to hand off raw responses to a custom handler,
  which in turns makes protocols like Websockets easier (Expose [Reader.t] and [Writer.t] via [`Switching_protocols] for websockets #488 by @msaffer).
• Set the user-agent by default if one is not provided (Set default user-agent #586 by @TheCBaH).
• Fix typo in the cohttp.js META file.
• Refresh use of the Re library to the latest version (Re no deprecate #602 by @rgrinberg).
• Rearrange the ppx dependencies to be more specific (cohttp depends on ppx_type_conv, not ppx_deriving #596 by @yomimono).
• Explicitly depend on sexplib in the Async backend (Add sexp_conv ppx #605 by @kevinqiu).