samples: add Terra samples

source: https://github.com/zdevito/terra/tree/master/tests

samples/Terra/calc.t

@@ -0,0 +1,33 @@
+function makecalcfn(inst)    
+    local stk = {}
+    for i,v in ipairs(inst) do
+        if type(v) == "number" then
+            table.insert(stk,`v)
+        else
+            local b = table.remove(stk)
+            local a = table.remove(stk)
+            
+            if v == "+" then
+                table.insert(stk,`a + b)
+            elseif v == "-" then
+                table.insert(stk,`a - b)
+            elseif v == "*" then
+                table.insert(stk,`a * b)
+            elseif v == "/" then
+                table.insert(stk,`a / b)
+            end
+        end
+    end
+    
+    local result = table.remove(stk)
+    
+    local terra wrapper()
+        return result
+    end
+    
+    return wrapper
+end
+
+local calcfn = makecalcfn({5,4,"*",5,"-",3,"+"})
+local test = require("test")
+test.eq(calcfn(),18)