Add a rudimentary animation system

[Dovyski]

I think the UI produced by cvui would benefit from some animation sugar, e.g. blinks, small fades, marching ants line, etc. This is definitely not the core of the lib, but I'm opening this issue to collect feedback and keep the idea alive.

Below is a gif of something I envision being possible with this simple animation system:

Creating aesthetically appealing UI should not be a burden, should be a breeze.

[thewoz]

cool!