add luacheck and ci workflow

.github/workflows/luacheck.yml

@@ -0,0 +1,17 @@
+name: luacheck
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@master
+    - name: apt
+      run: sudo apt-get install -y luarocks
+    - name: luacheck install
+      run: luarocks install --local luacheck
+    - name: luacheck run
+      run: $HOME/.luarocks/bin/luacheck ./

.luacheckrc

@@ -0,0 +1,22 @@
+-- unused_args = false
+-- allow_defined_top = true
+-- ignore = {"512"}
+
+globals = {
+	"digtron"
+}
+
+read_globals = {
+	-- Stdlib
+	string = {fields = {"split"}},
+	table = {fields = {"copy", "getn"}},
+	"VoxelManip",
+
+	-- Minetest
+	"minetest",
+	"vector", "ItemStack",
+	"dump", "VoxelArea",
+
+	-- Deps
+	"default"
+}