Add `MRB_METHOD_CACHE` description to `include/mrbconf.h`
/* exclude floating point numbers */
//#define MRB_WITHOUT_FLOAT
+/* add -DMRB_METHOD_CACHE to use method cache to improve performance */
+//#define MRB_METHOD_CACHE
+/* size of the method cache (need to be the power of 2) */
+//#define MRB_METHOD_CACHE_SIZE (1<<7)
+
/* add -DMRB_INT16 to use 16bit integer for mrb_int; conflict with MRB_INT64 */
//#define MRB_INT16
