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...

include/unicorn/unicorn.h

@@ -723,6 +723,18 @@ uc_err uc_context_save(uc_engine *uc, uc_context *context);
 UNICORN_EXPORT
 uc_err uc_context_restore(uc_engine *uc, uc_context *context);
 
+
+/*
+  Return the size needed to store the cpu context. Can be used to allocate a buffer
+  to contain the cpu context and directly call uc_context_save.
+
+  @uc: handle returned by uc_open()
+
+  @return the size for needed to store the cpu context as as size_t.
+*/
+UNICORN_EXPORT
+size_t uc_context_size(uc_engine *uc);
+
 #ifdef __cplusplus
 }
 #endif