core: move new object system to core module

this will allow a wider range of data structures (e.g. b_error, b_stream, b_stringstream) to make use
of the new object system, and other modules and library users can use the object system without
depending on the blue-object or blue-ds modules.

blue-ds will become a simple library of data structures (string, hashmap, etc), built on top of the
core object system.

core/class.h

@@ -0,0 +1,18 @@
+#ifndef _CLASS_H_
+#define _CLASS_H_
+
+#include <blue/core/error.h>
+#include <blue/core/misc.h>
+#include <stdint.h>
+
+struct b_type_registration;
+
+struct _b_class {
+	uint64_t c_magic;
+	const struct b_type_registration *c_type;
+};
+
+extern b_result b_class_instantiate(
+	struct b_type_registration *type, struct _b_class **out);
+
+#endif