 * Add top-left and bottom-right serifed variants for `K` and Cyrillic Ka (#1257).
 * Add characters:
   - LEFTWARDS ARROW WITH LOOP (`U+21AB`).
   - RIGHTWARDS ARROW WITH LOOP (`U+21AC`).
   - DOWNWARDS ZIGZAG ARROW (`U+21AF`).
   - LEFTWARDS TRIPLE ARROW (`U+21DA`).
   - RIGHTWARDS TRIPLE ARROW (`U+21DB`).
   - LEFTWARDS SQUIGGLE ARROW (`U+21DC`).
   - RIGHTWARDS SQUIGGLE ARROW (`U+21DD`).
   - RIGHTWARDS ARROW WITH TIP DOWNWARDS (`U+2B0E`) ... LEFTWARDS ARROW WITH TIP UPWARDS (`U+2B11`).
