Redcarpet v3.6.0

This release is not particularly heavy but brings a few improvements and fixes.

Improvements

• Avoid warnings running on Ruby 3.2+ (See #721).
• Consider <center> as a block-level element (See #702).
• Properly provide a third argument to the table_cell callback indicating whether the current cell is part of the header or not.
  The previous implementation with two parameters is still supported (See #604 and #605).

Fixes

• Match fence char and length when matching closing fence in fenced code blocks (Fixes #208).
• Fix anchor generation on titles with ampersands (Fixes #696).