Organized modules, added indirection for FFI vs extension loading (#10)

* mv src -> ext, lib -> src to be more in line with PHP module expectations

* Fixed dependency for ffi test

* Fixed path in format-check to C source

* CRT will now try the extension first, then FFI

config.m4

@@ -17,7 +17,7 @@ if test "$PHP_AWSCRT" != "no"; then
     PHP_SUBST(AWSCRT_SHARED_LIBADD)
 
     # Sources for the PHP extension itself
-    AWSCRT_SOURCES=src/*.c
+    AWSCRT_SOURCES=ext/*.c
     PHP_NEW_EXTENSION(awscrt, $AWSCRT_SOURCES, $ext_shared)
 fi