Support for docx export

[ldallolio]

Hi,
Thank you for this port, it really helped me!
I had to embed a Quill diff into a MS Word document, I would like to share some lines in case you want to add this export format :

from docx import Document
from delta import Delta
import io, base64

doc = Document()
for delta, attrs, index in Delta(test_ops).iter_lines():
    p = doc.add_paragraph()
    for op in delta.ops:
        insert_value = op.get('insert')
        attributes = op.get('attributes', {})
        if isinstance(insert_value, str) and insert_value:
            text = insert_value
            if 'header' in attrs:
                doc.add_heading(text, level=attrs['header'])
                continue
            if 'list' in attrs:
                list_style = 'List Number' if attrs['list'] == 'ordered' else 'List Bullet'
                if 'indent' in attrs:
                    list_style += f" {int(attrs['indent']) + 1}" 
                p.style = list_style
            run = p.add_run(text)
            if 'script' in attributes:
                if attributes['script'] == 'sub':
                    run.subscript = True
                if attributes['script'] == 'super':
                    run.superscript = True
            run.strike = attributes.get('strike', False)
            run.bold = attributes.get('bold', False) or attributes.get('strong', False)
            run.italic = attributes.get('italic', False) or attributes.get('em', False)
            run.underline = attributes.get('underline', False)
        elif isinstance(insert_value, dict):
            if 'image' in insert_value:
                image_content = insert_value["image"]
                prefix = "data:image/png;base64,"
                if image_content.startswith(prefix):
                    image_bytes = base64.b64decode(image_content[len(prefix):])
                image_stream = io.BytesIO(image_bytes)
                doc.add_picture(image_stream)

Here it is, nothing really complicated indeed :-) If you are interested, I could try to write something similar to the html exporter, just let me know ;)

All the best