Handle serialization of cpu context save (#1129)

* Handle the cpu context save in a more pythonic way, so the context can be serialized and reuse in an other process using the same emulator architecture and modes

* Fix type error ; mistakes a size_t uint64_t ; breaks in 32bit...

uc.c

@@ -1302,6 +1302,12 @@ uc_err uc_free(void *mem)
     return UC_ERR_OK;
 }
 
+UNICORN_EXPORT
+size_t uc_context_size(uc_engine *uc)
+{
+    return cpu_context_size(uc->arch, uc->mode);
+}
+
 UNICORN_EXPORT
 uc_err uc_context_save(uc_engine *uc, uc_context *context)
 {