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/common.inc

@@ -6,10 +6,24 @@
 use AWS\CRT\CRT as CRT;
 
 abstract class CrtTestCase extends PHPUnit_Framework_TestCase {
+    private static $crt = null;
+    public static function setUpBeforeClass() {
+        self::$crt = new CRT();
+    }
+
+    public static function tearDownAfterClass() {
+        self::$crt = null;
+    }
+
     // Ensure that after every test there are no errors in the CRT itself
     protected function assertPostConditions() {
         if (CRT::last_error()) {
             $this->fail("Test left an error on the stack: " . CRT::error_name(CRT::last_error()));
         }
     }
+
+    // shim expectException -> setExpectedException for PHPUnit 4.8.x
+    public function expectException($exceptionName) {
+        $this->setExpectedException($exceptionName);
+    }
 }