Creates sequence of bands for given range and padding.

Bands are evenly distributed intervals with padding.

Each band is a map with following keys:

* rstart - interval start
* rend - interval end
* point - selected point (default: midpoint)
* value - domain value

Input parameters are:

* bands - number of the bands (default: 1) or sequence of values
* padding-in - padding between bands (default: 0.0)
* padding-out - border padding (default: 0.0)
* align - position of the selected point (0.0 - left, 1.0 - right, 0.5 - midpoint, default)

Padding is calculated the same way as in `d3`. It's a proportion of the step.