Render markdown tables instead of printing their markup

[shellicar]

Summary

• A markdown table in a response renders as a table with a ruled header.
• Each column is as wide as its widest cell.
• Columns sit left, centre or right as the table's delimiter row asks.
• A table too wide for the terminal narrows its widest columns and wraps them.
• A fenced code block no longer mis-sizes its box around a link or a wide character.