Fix KHASH_DEFAULT_SIZE to KHASH_INITIAL_SIZE rename inconsistencies

Commit 250bf6edd renamed KHASH_DEFAULT_SIZE to KHASH_INITIAL_SIZE but
missed updating build_config files and documentation. Also restore the
default value in khash.h to 32, consistent with the documented default
and the profile hierarchy (MRB_CONSTRAINED_BASELINE_PROFILE reduces it
to 16).

include/mrbconf.h

@@ -139,7 +139,7 @@
 //#define MRB_GC_TURN_OFF_GENERATIONAL
 
 /* default size of khash table bucket */
-//#define KHASH_DEFAULT_SIZE 32
+//#define KHASH_INITIAL_SIZE 32
 
 /* allocated memory address alignment */
 //#define POOL_ALIGNMENT 4
@@ -208,8 +208,8 @@
 #  define MRB_NO_METHOD_CACHE
 # endif
 
-# ifndef KHASH_DEFAULT_SIZE
-#  define KHASH_DEFAULT_SIZE 16
+# ifndef KHASH_INITIAL_SIZE
+#  define KHASH_INITIAL_SIZE 16
 # endif
 
 # ifndef MRB_HEAP_PAGE_SIZE

include/mruby/khash.h

@@ -21,7 +21,7 @@ typedef uint32_t khint_t;
 typedef khint_t khiter_t;
 
 #ifndef KHASH_INITIAL_SIZE
-# define KHASH_INITIAL_SIZE 8
+# define KHASH_INITIAL_SIZE 32
 #endif
 #define KHASH_MIN_SIZE 8
 #define KHASH_SMALL_LIMIT 4