Add Lua code for chapter 3

03_recursion/lua/01_countdown.lua

@@ -0,0 +1,12 @@
+function countdown(i)
+    print(i)
+    -- base case
+    if i <= 0 then
+        return
+    -- recursive case
+    else
+        countdown(i - 1)
+    end
+end
+
+countdown(5)

03_recursion/lua/02_greet.lua

@@ -0,0 +1,16 @@
+function greet2(name)
+    print("how are you, " .. name .. "?")
+end
+
+function bye()
+    print("ok bye!")
+end
+
+function greet(name)
+    print("hello, " .. name .. "!")
+    greet2(name)
+    print("getting ready to say bye...")
+    bye()
+end
+
+greet("adit")

03_recursion/lua/03_factorial.lua

@@ -0,0 +1,9 @@
+function fact(x)
+    if x <= 1 then
+        return 1
+    else
+        return x * fact(x - 1)
+    end
+end
+
+print(fact(5))