Add ability to insert paragraphs and tables at specific positions. Upstream python-openxml#156 (23 comments).

API Design

• paragraph.insert_paragraph_after(text, style) — insert a new paragraph after this one
• paragraph.insert_paragraph_before() already exists — verify it works correctly
• paragraph.insert_table_after(rows, cols) — insert a table after this paragraph
• table.insert_paragraph_after(text, style) — insert after a table
• body.insert_element_before(new_element, reference_element) — low-level

Implementation

Uses lxml's addnext()/addprevious() on the underlying elements. The high-level methods create the element and position it.

Upstream issue: python-openxml#156