Minor JSON improvements

* Add 'json' to function names for consistency, e.g. duk__dec_xxx() to
  duk__json_dec_xxx().

* Remove 'JSON' from recursion limit error messages, it is usually
  apparent from the context and can be shared by CBOR encode/decode.

src-input/duk_strings.h

@@ -77,10 +77,12 @@
 /* JSON */
 #define DUK_STR_FMT_PTR                          "%p"
 #define DUK_STR_FMT_INVALID_JSON                 "invalid json (at offset %ld)"
-#define DUK_STR_JSONDEC_RECLIMIT                 "json decode recursion limit"
-#define DUK_STR_JSONENC_RECLIMIT                 "json encode recursion limit"
 #define DUK_STR_CYCLIC_INPUT                     "cyclic input"
 
+/* Generic codec */
+#define DUK_STR_DEC_RECLIMIT                     "decode recursion limit"
+#define DUK_STR_ENC_RECLIMIT                     "encode recursion limit"
+
 /* Object property access */
 #define DUK_STR_INVALID_BASE                     "invalid base value"
 #define DUK_STR_STRICT_CALLER_READ               "cannot read strict 'caller'"