HTTPS for the Async bindings (#35)

This PR adds HTTPS support to the Async runtime, based on `Async_ssl`.
Once `ocaml-tls` provides an Async runtime, we can add that one here.

CHANGES.md

@@ -53,6 +53,8 @@ Unreleased
   response body ([#34](https://github.com/anmonteiro/httpaf/pull/34)). This is
   a fix for an issue opened in the upstream repo:
   [inhabitedtype/httpaf#162](https://github.com/inhabitedtype/httpaf/issues/162)
+- httpaf-async: Add HTTPS support for the Async bindings
+  ([#35](https://github.com/anmonteiro/httpaf/pull/35)).
 
 httpaf (upstream) 0.6.5
 --------------

async/dune

@@ -1,7 +1,16 @@
 (library
- (name        httpaf_async)
+ (name httpaf_async)
  (public_name httpaf-async)
- (wrapped false)
  (libraries
-   async core faraday-async httpaf)
- (flags (:standard -safe-string)))
+  async
+  core
+  faraday-async
+  httpaf
+  (select
+   ssl_io.ml
+   from
+   (async_ssl -> ssl_io_real.ml)
+   (!async_ssl -> ssl_io_dummy.ml)))
+ (modules httpaf_async httpaf_async_intf ssl_io)
+ (flags
+  (:standard -safe-string)))