add options.output to customize output; v0.1.2
though performance dropped slightly:
| characters | type: 'string'     | type: 'int'        |
|------------|--------------------|--------------------|
| 1          | 30118.060164688082 | 35219.22556454687  |
| 3          | 21528.455996088192 | 34332.78032747127  |
| 11         | 12706.01136889286  | 33263.9365252798   |
| 29         | 6682.5287725458375 | 30127.59935611597  |
| 56         | 3825.320077808429  | 25660.769464552126 |