Added gruvbox colorscheme

Based on the vim gruvbox colorscheme. I made it as close as possible to the
original vim colors, but had to make some changes due to kakoune's highlighting
scheme being different than vim's.

colors/gruvbox.kak

@@ -0,0 +1,73 @@
+# gruvbox theme
+
+%sh{
+    gray="rgb:928374"
+    red="rgb:fb4934"
+    green="rgb:b8bb26"
+    yellow="rgb:fabd2f"
+    blue="rgb:83a598"
+    purple="rgb:d3869b"
+    aqua="rgb:8ec07c"
+    orange="rgb:fe8019"
+
+    bg="rgb:282828"
+    bg1="rgb:3c3836"
+    bg2="rgb:504945"
+    bg3="rgb:665c54"
+    bg4="rgb:7c6f64"
+
+    fg0="rgb:fbf1c7"
+    fg="rgb:ebdbb2"
+    fg2="rgb:d5c4a1"
+    fg3="rgb:bdae93"
+    fg4="rgb:a89984"
+
+    echo "
+        # Code highlighting
+        face value     ${purple}
+        face type      ${yellow}
+        face variable  ${blue}
+        face module    ${green}
+        face function  default
+        face string    ${green}
+        face keyword   ${red}
+        face operator  default
+        face attribute ${orange}
+        face comment   ${gray}
+        face meta      ${aqua}
+        face builtin   default+b
+
+        # Markdown highlighting
+        face title     ${green}+b
+        face header    ${orange}
+        face bold      ${fg}+b
+        face italic    ${fg3}
+        face mono      ${fg4}
+        face block     default
+        face link      default
+        face bullet    default
+        face list      default
+
+        face Default            ${fg},${bg}
+        face PrimarySelection   ${fg},${blue}
+        face SecondarySelection ${bg},${blue}
+        face PrimaryCursor      ${bg},${fg}
+        face SecondaryCursor    ${bg},${fg}
+        face LineNumbers        ${bg4}
+        face LineNumberCursor   ${yellow},${bg1}
+        face MenuForeground     ${bg2},${blue}
+        face MenuBackground     default,${bg2}
+        face MenuInfo           ${bg}
+        face Information        ${bg},${fg}
+        face Error              default,${red}
+        face StatusLine         default
+        face StatusLineMode     ${yellow}+b
+        face StatusLineInfo     ${purple}
+        face StatusLineValue    ${red}
+        face StatusCursor       ${bg},${fg}
+        face Prompt             ${yellow}
+        face MatchingChar       default+b
+        face BufferPadding      ${bg2},${bg}
+        face Whitespace         ${bg2}
+    "
+}