Contribute new 8-bit theme: Ansi 16

.gitmodules

@@ -236,3 +236,6 @@
 [submodule "assets/syntaxes/02_Extra/Dart"]
 	path = assets/syntaxes/02_Extra/Dart
 	url = https://github.com/elMuso/Dartlight.git
+[submodule "assets/themes/ansi16"]
+	path = assets/themes/ansi16
+	url = https://github.com/chtenb/ansi16

README.md

@@ -432,6 +432,7 @@ even when truecolor support is available:
 - `base16-256` is designed for [base16-shell](https://github.com/chriskempson/base16-shell).
   It replaces certain bright colors with 8-bit colors from 16 to 21. **Do not** use this simply
   because you have a 256-color terminal but are not using base16-shell.
+- `terminal-ansi16` looks decent on any terminal. It uses 4-bit colors (3-bit colors plus bright variants) in accordance with the [Ansi 16](https://github.com/chtenb/ansi16) guidelines. If your editor and terminal have the same Ansi 16 color theme, their syntax highlighting will match.
 
 Although these themes are more restricted, they have three advantages over truecolor themes. They:
 

tests/assets.rs

@@ -36,6 +36,10 @@ fn all_themes_are_present() {
             "base16-256",
             "gruvbox-dark",
             "gruvbox-light",
+            "material-ansi16",
+            "noctis-lux-ansi16",
+            "synthwave-material-ansi16",
+            "terminal-ansi16",
             "zenburn"
         ]
     );