Fix/lua no funcs known (#15)

* lua fixes:

- fix lua function calling, didn't work in the last
releases (regression)
- add lua funcs which don't modify the stack (for converters etc)
- added better lua examples

main.go

@@ -30,7 +30,7 @@ import (
 	lua "github.com/yuin/gopher-lua"
 )
 
-const VERSION string = "2.0.5"
+const VERSION string = "2.0.6"
 
 const Usage string = `This is rpn, a reverse polish notation calculator cli.
 
@@ -98,8 +98,9 @@ func main() {
 	// our config file is interpreted  as lua code, only functions can
 	// be defined, init() will be called by InitLua().
 	if _, err := os.Stat(configfile); err == nil {
-		I := InitLua(configfile, enabledebug)
-		calc.SetInt(I)
+		luarunner := NewInterpreter(configfile, enabledebug)
+		luarunner.InitLua()
+		calc.SetInt(luarunner)
 	}
 
 	if len(flag.Args()) > 1 {