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+HTTP2 with libcurl
+
+ Spec: http://www.rfc-editor.org/rfc/rfc7540.txt
+
+ Document explaining it: http://daniel.haxx.se/http2/
+
+ Build prerequisites
+  - nghttp2
+  - OpenSSL, NSS, GnutTLS or PolarSSL with a new enough version
+
+ nghttp2 (https://github.com/tatsuhiro-t/nghttp2)
+
+  libcurl uses this 3rd party library for the low level protocol handling
+  parts. The reason for this is that HTTP/2 is much more complex at that layer
+  than HTTP/1.1 (which we implement on our own) and that nghttp2 is an already
+  existing and well functional library.
+
+  We require at least version 1.0.0.
+
+ Over an http:// URL
+
+  If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2_0, libcurl will
+  include an upgrade header in the initial request to the host to allow
+  upgrading to http2.
+
+  Possibly we can later introduce an option that will cause libcurl to fail if
+  not possible to upgrade. Possibly we introduce an option that makes libcurl
+  use http2 at once over http://
+
+ Over an https:// URL
+
+  If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2_0, libcurl will use
+  ALPN (or NPN) to negotiate which protocol to continue with. Possibly
+  introduce an option that will cause libcurl to fail if not possible to use
+  http2.  Consider options to explicitly disable ALPN and/or NPN.
+
+  ALPN is the TLS extension that http2 is expected to use. The NPN extension
+  is for a similar purpose, was made prior to ALPN and is used for SPDY so
+  early http2 servers are implemented using NPN before ALPN support is
+  widespread.
+
+SSL libs
+
+  The challenge is the ALPN and NPN support and all our different SSL
+  backends. You may need a fairly updated SSL library version for it to
+  provide the necessary TLS features. Right now we support:
+
+    OpenSSL:  ALPN and NPN
+    NSS:      ALPN and NPN
+    GnuTLS:   ALPN
+    PolarSSL: ALPN
+
+Multiplexing
+
+  Starting in 7.43.0, libcurl fully supports HTTP/2 multiplexing, which is the
+  term for doing multiple independent transfers over the same physical TCP
+  connection.
+
+  To take advantage of multiplexing, you need to use the multi interface and
+  set CURLMOPT_PIPELINING to CURLPIPE_MULTIPLEX. With that bit set, libcurl
+  will attempt to re-use existing HTTP/2 connections and just add a new stream
+  over that when doing subsequent parallel requests.
+
+  While libcurl sets up a connection to a HTTP server there is a period during
+  which it doesn't know if it can pipeline or do multiplexing and if you add
+  new transfers in that period, libcurl will default to start new connections
+  for those transfers. With the new option CURLOPT_PIPEWAIT (added in 7.43.0),
+  you can ask that a transfer should rather wait and see in case there's a
+  connection for the same host in progress that might end up being possible to
+  multiplex on. It favours keeping the number of connections low to the cost
+  of slightly longer time to first byte transfered.
+
+Applications
+
+  We hide http2's binary nature and convert received http2 traffic to headers
+  in HTTP 1.1 style. This allows applications to work unmodified.
+
+curl tool
+
+  curl offers the --http2 command line option to enable use of http2
+
+HTTP Alternative Services
+
+  Alt-Svc is a suggested extension with a corresponding frame (ALTSVC) in
+  http2 that tells the client about an alternative "route" to the same content
+  for the same origin server that you get the response from. A browser or
+  long-living client can use that hint to create a new connection
+  asynchronously.  For libcurl, we may introduce a way to bring such clues to
+  the applicaton and/or let a subsequent request use the alternate route
+  automatically. Spec:
+  http://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-05
+
+TODO:
+
+  - Provide API to set priorities / dependencies of individual streams
+
+  - Implement "prior-knowledge" HTTP/2 connecitons over clear text so that
+    curl can connect with HTTP/2 at once without 1.1+Upgrade.
+