Speeding up `GMPShortener` by using `gmp_init()` to convert a UUID from HEX to DEC
Speeding up `GMPShortener` by using `gmp_init()` to convert a UUID from HEX to DEC

Went from:

```
run 1343c4715fc30988367a16d986ea678aa75a54ce
Date:    2020-05-19T12:55:51+02:00
Branch:  feature/faster-shortening
Tag:     first_gmp_shortener
Scale:   3 subjects, 15 iterations, 15 revolutions
Summary: (best [mean] worst) = 142.000 [2,718.547] 155.200 (μs)
         ⅀T: 40,778.200μs μRSD/r: 2.406%
```

to

```
run 1343c473bee6b300102b7ec282757c253552025d
Date:    2020-05-19T13:25:10+02:00
Branch:  feature/faster-shortening
Tag:     gmp_number_conversion_from_hex
Scale:   3 subjects, 15 iterations, 15 revolutions
Summary: (best [mean] worst) = 10.800 [1,997.067] 11.200 (μs)
         ⅀T: 29,956.000μs μRSD/r: 1.970%
```

mgrajcarek/uuid-shortener