Mutation generation for `dna-codec` library.

[corbanvilla]

Helper function to help users create mutation rates for their species.

Should allow passing an enum:

enum MutationRatePercent {
    100,
    50,
    25,
    12.5,
    6.25,
    3.125,
    1.5625,
    0.78125,
    0.390625,
    0.1953125,
    0.09765625,
    0.048828125,
    0.0244140625,
    0.0122070312,
    0.0061035156,
    0.0030517578,
    0.0015258789,
    0.0007629395
}