Implement ale.pad in Lua

test/lua/ale_pad_spec.lua

@@ -0,0 +1,13 @@
+local eq = assert.are.same
+local ale = require("ale")
+
+describe("ale.pad", function()
+    it("should pad non-empty strings", function()
+        eq(" foo", ale.pad("foo"))
+    end)
+
+    it("should return empty strings for nil or empty strings", function()
+        eq("", ale.pad(nil))
+        eq("", ale.pad(""))
+    end)
+end)