add macro for ioMode of getStr

include/mcl/bn.h

@@ -112,7 +112,10 @@ typedef struct {
 
 #include <mcl/curve_type.h>
 
+#define MCLBN_IO_EC_AFFINE 0
+#define MCLBN_IO_EC_PROJ 1024
 #define MCLBN_IO_SERIALIZE_HEX_STR 2048
+
 // for backword compatibility
 enum {
 	mclBn_CurveFp254BNb = 0,
@@ -434,7 +437,7 @@ MCLBN_DLL_API void mclBnGT_invGeneric(mclBnGT *y, const mclBnGT *x);
 */
 MCLBN_DLL_API void mclBnGT_powGeneric(mclBnGT *z, const mclBnGT *x, const mclBnFr *y);
 /*
-	pow for only {x|x^r = 1} in Fp12 by GLV method
+	pow for only {x|x^r = 1} in GT by GLV method
 	the value generated by pairing satisfies the condition
 */
 MCLBN_DLL_API void mclBnGT_pow(mclBnGT *z, const mclBnGT *x, const mclBnFr *y);