Clean up lua docs scripts

- ldoc is now a git submodule
- ldoc can be installed using scripts/install.{sh,ps1}
- lua docs can be build using scripts/build.{sh,ps1}
- all lua docs-related files now reside inside of the docs folder

docs/scripts/serve.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"
+cd "$DIR/.."
+
+if ! command -v "python3" &> /dev/null; then
+  echo "python3 not found"
+  exit 1
+fi
+
+python3 -m http.server -d html