Shift (the support of) a ddf distribution by the specified amount.
Examples
# Distribution for a simple symmetric random walk with
# step size 1 of length 4, centered at 3 (instead of 0)
shift(conv_n(rademacher(), 4), 3)
#> 4-fold convolution of Rademacher distribution, shifted by 3
#>
#> Support:
#> [1] -1 1 3 5 7
#>
#> Probabilities:
#> [1] 0.0625 0.2500 0.3750 0.2500 0.0625
