Update period and digits range

[paolostivanin]

• period must be 0 < period <= 120
• digits must be 3 <= digits <= 15
• fix Add support for custom digits #20

[magiruuvelvet]

i noticed a segfault after playing around with the new changes.

i needed to change this, otherwise it segfaults

static int64_t DIGITS_POWER[] = {1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000,
                                 10000000000, 100000000000, 1000000000000, 10000000000000, 100000000000000};

the digit count is still limited to 8 because of this

[paolostivanin]

I'll have a look at it next week! Thanks for the heads-up

[paolostivanin]

@magiruuvelvet how did you manage to get the segfault? I couldn't reproduce the issue...