Alpha-gradient fade-out on one or more edges. :edges is
:all or a list drawn from :top, :bottom, :left,
:right. :length is either an integer pixel count or a
float fraction of the relevant dimension. Maps to
Cloudinary's e_fade[:N] (N interpreted as a percentage).
Summary
Types
@type edge() :: :top | :bottom | :left | :right
@type t() :: %Image.Plug.Pipeline.Ops.Fade{ edges: [edge()] | :all, length: pos_integer() | float() }