Add Transaction type to Python bindings, get first tests working.

src/runtime/python/ffi.h

@@ -1,5 +1,5 @@
-#ifndef PYPGF_MARSHALLER_H_
-#define PYPGF_MARSHALLER_H_
+#ifndef PYPGF_FFI_H_
+#define PYPGF_FFI_H_
 
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
@@ -21,4 +21,4 @@ PyObject *PyUnicode_FromPgfText(PgfText *text);
 extern PgfUnmarshaller unmarshaller;
 extern PgfMarshaller marshaller;
 
-#endif // PYPGF_MARSHALLER_H_
+#endif // PYPGF_FFI_H_