add git-tools.kak, with experimental git diff display as line flags

src/rc/git-tools.kak

@@ -0,0 +1,25 @@
+decl line-flag-list git_diff_flags
+
+def git-diff-update-buffer %{ %sh{
+    added_lines=""
+    removed_lines=""
+    git diff -U0 $kak_bufname | {
+        line=0
+        flags="0:red:."
+        while read; do
+            if [[ $REPLY =~ ^---.* ]]; then
+                continue
+            elif [[ $REPLY =~ ^@@.-[0-9]+(,[0-9]+)?.\+([0-9]+)(,[0-9]+)?.@@.* ]]; then
+                line=${BASH_REMATCH[2]}
+            elif [[ $REPLY =~ ^\+ ]]; then
+                flags="$flags,$line:green:+"
+                ((line++))
+            elif [[ $REPLY =~ ^\- ]]; then
+                flags="$flags,$line:red:-"
+            fi
+        done
+        echo "setb git_diff_flags '$flags'"
+    }
+}}
+
+def git-diff-show %{ addhl flag_lines black git_diff_flags; git-diff-update-buffer }