Input Stream bindings (#18)

* Initial aws_input_stream <-> php_stream implementation

* Added comments about useful references

* updated aws-crt-ffi to get latest aws-lc, faster builds

* Fixed inconsistency between PHP5/7 versions of php_stream_from_zval

src/AWS/CRT/HTTP/Message.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace AWS\CRT\HTTP;
+
+abstract class Message {
+    private $path = "";
+    private $query = [];
+    private $headers = [];
+
+    public function __construct($path, $query = [], $headers = []) {
+        $this->path = $path;
+        $this->query = $query;
+        $this->headers = $headers;
+    }
+}
+
+class Request extends Message {
+    private $body_stream = null;
+
+    public function __construct($path, $query = [], $headers = [], $body_stream = null) {
+        parent::__construct($path, $query, $headers);
+        $this->body_stream = $body_stream;
+    }
+}
+
+class Response extends Message {
+    private $status_code;
+
+    public function __construct($path, $headers, $status_code) {
+        parent::__construct($path, [], $headers);
+        $this->status_code = $status_code;
+    }
+}