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

Makefile

@@ -5,14 +5,14 @@ CFLAGS += -Wall -I$(SRCDIR)/kiwi
 LIBFLAG := -shared
 LIB_EXT := so
 
-ifeq ($(findstring gcc, $(CC)), gcc)
-  CXX := $(subst gcc, g++, $(CC))
+ifeq ($(findstring gcc,$(CC)),gcc)
+  CXX := $(subst gcc,g++,$(CC))
   CXXFLAGS += -std=c++14
   ifneq ($(SANITIZE),)
     CFLAGS += -fsanitize=undefined -fsanitize=address
   endif
 else
-ifeq ($(CC), clang)
+ifeq ($(CC),clang)
   CXX := clang++
   CXXFLAGS += -std=c++14
   ifneq ($(SANITIZE),)