Phase D.15: Row.height — set and get table row height

Set/get table row height and height rule (auto, exact, at-least).

- row.height — Emu/Pt value or None (auto)
- row.height_rule — WD_ROW_HEIGHT_RULE enum (AUTO, AT_LEAST, EXACTLY)

XML: w:trPr > w:trHeight with w:val (twips) and w:hRule attribute.

Upstream: #96 (15 comments)