Convert Token from enum to struct (#256)

* convert Token from enum to struct

* private setter for components

* updated CHANGELOG

Sources/Node.swift

@@ -62,7 +62,7 @@ public class VariableNode : NodeType {
   let elseExpression: Resolvable?
 
   class func parse(_ parser:TokenParser, token:Token) throws -> NodeType {
-    var components = token.components()
+    var components = token.components
 
     func hasToken(_ token: String, at index: Int) -> Bool {
       return components.count > (index + 1) && components[index] == token