[8_11] boost performance of api converting number to hexadecimal string

[jingkaimori]

Performance

to_hex faster 50%, as_hexadecimal faster 82%!!!

Before

complexityN	ns/op	op/s	err%	total	benchmark
1	3.03	329,610,514.51	2.3%	0.02	convert hexadecimal string to int
1	12.77	78,320,857.02	1.9%	0.06	convert signed int to hexadecimal string
1	13.15	76,026,752.24	1.1%	0.06	convert unsigned int to hexadecimal string
2	3.91	255,599,303.35	4.7%	0.02	convert hexadecimal string to int
2	12.69	78,811,782.13	1.0%	0.06	convert signed int to hexadecimal string
2	47.51	21,049,513.78	2.8%	0.23	convert unsigned int to hexadecimal string
3	4.85	206,384,036.36	1.6%	0.02	convert hexadecimal string to int
3	12.81	78,044,226.04	0.7%	0.06	convert signed int to hexadecimal string
3	74.44	13,434,353.45	0.7%	0.36	convert unsigned int to hexadecimal string
4	5.88	170,029,870.91	2.3%	0.03	convert hexadecimal string to int
4	48.58	20,584,946.78	3.1%	0.24	convert signed int to hexadecimal string
4	108.33	9,231,414.46	0.5%	0.52	convert unsigned int to hexadecimal string
5	6.70	149,337,147.16	0.5%	0.03	convert hexadecimal string to int
5	48.16	20,763,956.26	1.3%	0.23	convert signed int to hexadecimal string
5	148.89	6,716,357.71	0.2%	0.72	convert unsigned int to hexadecimal string

After

complexityN	ns/op	op/s	err%	total	benchmark
1	2.95	339,258,986.45	0.8%	0.02	convert hexadecimal string to int
1	17.74	56,374,077.33	1.5%	0.08	convert signed int to hexadecimal string
1	14.38	69,547,781.82	0.9%	0.07	convert unsigned int to hexadecimal string
2	3.94	253,905,312.41	3.4%	0.02	convert hexadecimal string to int
2	17.42	57,406,505.14	1.2%	0.08	convert signed int to hexadecimal string
2	15.57	64,211,588.80	0.6%	0.08	convert unsigned int to hexadecimal string
3	5.76	173,703,719.01	2.6%	0.03	convert hexadecimal string to int
3	17.49	57,190,688.69	1.1%	0.09	convert signed int to hexadecimal string
3	17.21	58,097,326.85	1.3%	0.08	convert unsigned int to hexadecimal string
4	5.89	169,673,236.32	2.5%	0.03	convert hexadecimal string to int
4	21.83	45,811,805.23	1.0%	0.11	convert signed int to hexadecimal string
4	19.27	51,898,451.76	1.4%	0.09	convert unsigned int to hexadecimal string
5	6.73	148,631,690.89	1.9%	0.03	convert hexadecimal string to int
5	22.18	45,085,309.87	1.1%	0.11	convert signed int to hexadecimal string
5	22.65	44,143,155.21	0.4%	0.11	convert unsigned int to hexadecimal string