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)

config.m4

@@ -3,7 +3,8 @@ dnl * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 dnl * SPDX-License-Identifier: Apache-2.0.
 dnl
 
-PHP_ARG_WITH(awscrt)
+PHP_ARG_WITH(awscrt, for AWS Common Runtime support,
+    [  --with-awscrt         Include awscrt support])
 
 if test "$PHP_AWSCRT" != "no"; then
     # force lib paths to be absolute, or PHP will mangle them
@@ -23,8 +24,7 @@ if test "$PHP_AWSCRT" != "no"; then
     PHP_SUBST(AWSCRT_SHARED_LIBADD)
 
     # Sources for the PHP extension itself
-    AWSCRT_SOURCES=ext/*.c
+    AWSCRT_SOURCES=ext/awscrt.c
     PHP_NEW_EXTENSION(awscrt, $AWSCRT_SOURCES, $ext_shared)
+    PHP_ADD_MAKEFILE_FRAGMENT
 fi
-
-PHP_ADD_MAKEFILE_FRAGMENT