Update API, naming, and tests. Split data models to be independent.

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

Author: cau-git

README.md

@@ -65,7 +65,7 @@ pip install docling-parse
 Convert a PDF (look in the [visualize.py](docling_parse/visualize.py) for a more detailed information)
 
 ```python
-from docling_parse.document import SegmentedPdfPageLabel
+from docling_parse.document import TextCellUnit
 from docling_parse.pdf_parser import DoclingPdfParser, PdfDocument
 
 parser = DoclingPdfParser()
@@ -78,11 +78,11 @@ pdf_doc: PdfDocument = parser.load(
 for page_no, pred_page in pdf_doc.iterate_pages():
 
     # iterate over the word-cells
-    for word in pred_page.yield_cells(label=SegmentedPdfPageLabel.WORD):
-        print(word.rect, ": ", word.text)    
+    for word in pred_page.iterate_cells(unit_type=TextCellUnit.WORD):
+        print(word.rect, ": ", word.text)
 
-    # create a PIL image with the char cells
-    img = pred_page.render(label=SegmentedPdfPageLabel.CHAR)
+        # create a PIL image with the char cells
+    img = pred_page.render_as_image(label=TextCellUnit.CHAR)
     img.show()
 ```