docsite: Use evy editor in docs

[juliaogris]

```evy blocks => evy editor
```evy:out    => target output
```evy:in     => source for sample imput

We might have update evy:out to evy-out as evy:out is not a valid CSS class name.

Add a button to revert to initial code.

[juliaogris]

Here's a different approach:

```evy            => evy syntax coloring, on linked output
```evy:1          => evy syntax coloring, no editor
```evy:edit:1     => evy editor
```evy:out:1      => evy editor
```evy:drawing:1  => target output
```evy:in:1       => source for sample imput