Restored FFI to working order (#28)

* Restored FFI to working order

* Disabled incompatible tests, fixed string conversion

* Use extension_loaded instead of checking PHP version

* Added better checks for FFI

* Do not build FFI deps if no FFI is present

builder.json

@@ -32,6 +32,6 @@
         "NO_INTERACTION": "1"
     },
     "test_steps": [
-        ["make", "test"]
+        ["./ci-test.sh"]
     ]
 }