Replace most of the examples in readme with gifs

[FichteFoll]

Gifs (or rather videos, but github doesn't support <video> embeds) are a lot easier to grasp than the bulk of text we have currently.

[jbrooksuk]

Agreed, this can be easily done too.

[scholtes]

What value would this add? The documentation as-is acts as a searchable reference.

[FichteFoll]

Improve understanding of the examples through visualization of the actual effects. The example format strings would still be included as text, but the two multi-line code blocks would be replaced by a single gif.