Log Message:
spleen: update to 1.8.1.

Spleen 1.8.1 (2020-07-16)

- Center tilde vertically for all sizes, as modern fonts do
- Add black triangles in the 25E2-25E5 range
- Add single angle quotation mark characters
- Add white and black circle characters
- Add inverse bullet and inverse white circle characters
- Add 'A', 'a', 'O', 'o', 'U', 'u' characters with caron
- Add 'I', 'i', 'G', 'g', 'j' characters with caron
- Add 'H', 'h', 'K', 'k', characters with caron
- Add 'E' and 'e' characters with cedilla
- Add 'A', 'a', 'E', 'e', 'I', 'i', 'O', 'o', 'R', 'r', 'U', 'u' with
  double grave
- Add "almost equal to" character
- Add 'G' and 'g' characters with acute accent
- Add 'O' and 'o' characters with stroke and acute
- Add double vertical bar and double exclamation mark characters
- Add stand alone breve, dot above, ogonek, small tilde, and double
  acute accent