http: introduce AWS HTTP v4 Signature

It is a security process for HTTP.

It doesn't seems to be standard, but it is used by some cloud providers.

Aws:
https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html
Outscale:
https://wiki.outscale.net/display/EN/Creating+a+Canonical+Request
GCP (I didn't test that this code work with GCP though):
https://cloud.google.com/storage/docs/access-control/signing-urls-manually

most of the code is in lib/http_v4_signature.c

Information require by the algorithm:
- The URL
- Current time
-  some prefix that are append to some of the signature parameters.

The data extracted from the URL are: the URI, the region,
the host and the API type

example:
https://api.eu-west-2.outscale.com/api/latest/ReadNets
        ~~~ ~~~~~~~~               ~~~~~~~~~~~~~~~~~~~
        ^       ^                          ^
       /         \                        URI
   API type     region

Small description of the algorithm:
- make canonical header using content type, the host, and the date
- hash the post data
- make canonical_request using custom request, the URI,
  the get data, the canonical header, the signed header
  and post data hash
- hash canonical_request
- make str_to_sign using one of the prefix pass in parameter,
  the date, the credential scope and the canonical_request hash
- compute hmac from date, using secret key as key.
- compute hmac from region, using above hmac as key
- compute hmac from api_type, using above hmac as key
- compute hmac from request_type, using above hmac as key
- compute hmac from str_to_sign using above hmac as key
- create Authorization header using above hmac, prefix pass in parameter,
  the date, and above hash

Signed-off-by: Matthias Gatto <matthias.gatto@outscale.com>

Closes #5703

docs/libcurl/symbols-in-versions

@@ -29,6 +29,7 @@ CURLAUTH_NONE                   7.10.6
 CURLAUTH_NTLM                   7.10.6
 CURLAUTH_NTLM_WB                7.22.0
 CURLAUTH_ONLY                   7.21.3
+CURLAUTH_AWS_SIGV4              7.75.0
 CURLCLOSEPOLICY_CALLBACK        7.7
 CURLCLOSEPOLICY_LEAST_RECENTLY_USED 7.7
 CURLCLOSEPOLICY_LEAST_TRAFFIC   7.7
@@ -668,6 +669,7 @@ CURLOPT_USERAGENT               7.1
 CURLOPT_USERNAME                7.19.1
 CURLOPT_USERPWD                 7.1
 CURLOPT_USE_SSL                 7.17.0
+CURLOPT_AWS_SIGV4               7.75.0
 CURLOPT_VERBOSE                 7.1
 CURLOPT_WILDCARDMATCH           7.21.0
 CURLOPT_WRITEDATA               7.9.7