Add when option for loops cycles

[Miika Alonen]

Add when option for loops. Something that could be run for every 6 cycle or last 2 cycles etc.

For example:

z1 "1234", seed: 2, when: {
cycles: 4,
last: 2
do: { offset: 2 }
}

[Miika Alonen]

Added in 1.1 but not documented yet.

[Miika Alonen]

Refactored and documented: https://github.com/amiika/ziffers/wiki/Loop#cycle-options-and-transformations