Implemented async callbacks to PHP regardless of thread model, Sigv4 signing (#24)

* Updated to get latest aws-crt-ffi

* Added implementation for signing_result

* Added main thread queue and callback queueing to signing process

* Updated to get support for date on signing_config_aws

* added date support to SigningConfigAWS, fixed up reference issues on http message signing

* Broke C code into separate files, moved common stuff to php_aws_crt.h

* Use a unity build to make PHP do the right thing with our lib

* Updated aws-crt-ffi to v0.1.3 to get sigv4 changes

* Added CRT::isAvailable for safe runtime detection of CRT

* Fixed up test resource safety, added tests to prove it

* Added CI jobs for every version of PHP on linux (#26)

tests/ErrorTest.php

@@ -6,14 +6,6 @@
 use AWS\CRT\CRT;
 
 final class ErrorTest extends PHPUnit_Framework_TestCase {
-    private static $crt = null;
-    public static function setUpBeforeClass() {
-        self::$crt = new CRT();
-    }
-
-    public static function tearDownAfterClass() {
-        self::$crt = null;
-    }
 
     public function testNoInitialError() {
         $this->assertEquals(0, CRT::last_error());