Convert Token from enum to struct (#256)

* convert Token from enum to struct

* private setter for components

* updated CHANGELOG

Sources/NowTag.swift

@@ -9,7 +9,7 @@ class NowNode : NodeType {
   class func parse(_ parser:TokenParser, token:Token) throws -> NodeType {
     var format:Variable?
 
-    let components = token.components()
+    let components = token.components
     guard components.count <= 2 else {
       throw TemplateSyntaxError("'now' tags may only have one argument: the format string.")
     }