Minor fixes and API change

- fix stupid spaces in Makefile
- small type annotation fix
- Modify Expression constructor API to use varargs
- Update kiwi.lua to support future C API module

spec/constraint_spec.lua

@@ -42,7 +42,7 @@ describe("Constraint", function()
          c = kiwi.Constraint(lhs / 2, nil, "LE", kiwi.strength.MEDIUM)
          assert.equal("0.5 foo + 0.5 <= 0 | medium", tostring(c))
 
-         c = kiwi.Constraint(lhs, kiwi.Expression(nil, 3), "GE", kiwi.strength.WEAK)
+         c = kiwi.Constraint(lhs, kiwi.Expression(3), "GE", kiwi.strength.WEAK)
          assert.equal("1 foo + -2 >= 0 | weak", tostring(c))
       end)
 
@@ -68,7 +68,7 @@ describe("Constraint", function()
       end)
       it("combines lhs and rhs", function()
          local v2 = kiwi.Var("bar")
-         local rhs = kiwi.Expression({ 5 * v2, 3 * v }, 3)
+         local rhs = kiwi.Expression(3, 5 * v2, 3 * v)
          local c = kiwi.Constraint(lhs, rhs)
 
          local e = c:expression()