Add examples

Editor.js now has a NestedList tool which (unfortunately) uses the
same block name "list" as the simple List block tool.

As such, this adds support to nested ul and ol tags following
the output showed in
https://github.com/editor-js/nested-list#output-data

Here's an example of such output data:
```json
{
    "type" : "list",
    "data" : {
        "style" : "unordered",
        "items" : [
            {
              "content": "Apples",
              "items": [
                {
                  "content": "Red",
                  "items": []
                },
                {
                  "content": "Green",
                  "items": []
                },
              ]
            },
            {
              "content": "Bananas",
              "items": [
                {
                  "content": "Yellow",
                  "items": []
                },
              ]
            },
        ]
    }
}
```

Closes #30

This block is just a variation of the Image block, where the `file`
is replaced by a simple `url` string.

Closes #23

The new format assumes that withHeadings property only applies to
the first row.

This makes our table renderer compatible with both formats.

Closes #34

…-image

Adds support to SimpleImage

Support NestedList

Fix Table block with new format