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/install.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"
+cd "$DIR/.."
+
+lua_binary="${LUA_BINARY:-lua}"
+
+if ! command -v "$lua_binary" &> /dev/null; then
+  if [[ -z "${LUA_BINARY+x}" ]]; then
+    echo "lua binary not found; please set \$LUA_BINARY manually."
+  else
+    echo "lua binary not found: $lua_binary"
+  fi
+  exit 1
+fi
+
+if ! command -v "$lua_binary" &> /dev/null; then
+  echo "luarocks not found"
+  exit 1
+fi
+
+lua_version="$("$lua_binary" -v | grep -Po '^Lua \K(\d+)\.(\d+)')"
+echo "Detected lua version $lua_version"
+
+# Install dependencies (npm style)
+# NOTE: you need to have lua header files installed.
+# On debian-based distros: apt install libluaX.X-dev
+
+luarocks_args=(
+  "--tree"
+  "$PWD/lua_modules"
+  "--lua-version"
+  "$lua_version"
+)
+
+(
+  cd libs/ldoc
+  luarocks ${luarocks_args[@]} make
+)