[feature] lossless transformer

[gera2ld]

Parse Markdown to a lossless node tree, inserting empty nodes where needed to keep all hierarchical information.

Input:

p0

### h0.1

p1

## h1

p2

- l1
- l2

p3

```
code block
```

### h1.1

p4

Output:

- <empty>
  - <empty>
    - p0
  - h0.1
    - p1
- h1
  - <empty>
    - p2
    - ul
      - l1
      - l2
    - p3
    - code block
  - h1.1
    - p4

Pros:

• there will be no more confusion with subheadings and other nodes of the same parents (e.g. paragraph before a subheading, p2 and h1.1 in the example above).
• add possibility to edit content on the tree and reflect to the Markdown