Feature footnote support

[tiberlas]

Hi, I've created footnote support. To the API I added functions:

• Can read footnotes from a paragraph as a list. The footnote object contains footnote reference id and paragraphs.

  doc = Document('test.docx')
  paragraph = doc.paragraphs[0]
  footnotes = paragraph.footnotes
  for footnote in footnotes:
  print(f'footnote reference id: {footnote.id}')
  print(f'this footnote has paragraphs: {len(footnote.paragraphs)}')

• Can access all footnotes in a document as a list where the list index is footnote reference id for that footnote

  doc = Document('test.docx')
  for footnote in doc.footnotes:
  print(f'footnote reference id: {footnote.id}')
  print(f'this footnote has paragraphs: {len(footnote.paragraphs)}')

• Can add a footnote to the end of a paragraph. The footnote reference id is calculated based on the other footnotes in the document. On a created footnote object you can add paragraphs.

  doc = Document('test.docx')
  paragraph = doc.paragraphs[0]
  new_footnote = paragraph.add_footnote()
  new_footnote.add_paragraph('paragraph in footnote')

• Can read and change footnote properties in a section.

  doc = Document('test.docx')
  s = doc.section[0]
  print(s.footnote_position)
  print(s.footnote_number_format)
  print(s.footnote_numbering_start_value)
  print(s.footnote_numbering_restart_location)
  s.footnote_position = 'beneathText'
  s.footnote_number_format = 'hex'
  s.footnote_numbering_start_value = 4
  s.footnote_numbering_restart_location = 'eachPage'