replaced Token with Lexeme protocol on TemplateSyntaxError

Sources/Errors.swift

@@ -17,3 +17,29 @@ public class TemplateDoesNotExist: Error, CustomStringConvertible {
     return "Template named `\(templates)` does not exist. No loaders found"
   }
 }
+
+public struct TemplateSyntaxError : Error, Equatable, CustomStringConvertible {
+  public let description:String
+  var lexeme: Lexeme?
+  
+  public init(_ description:String) {
+    self.description = description
+  }
+  
+  public static func ==(lhs:TemplateSyntaxError, rhs:TemplateSyntaxError) -> Bool {
+    return lhs.description == rhs.description
+  }
+  
+}
+
+extension Range where Bound == String.Index {
+  internal static var unknown: Range {
+    return "".range
+  }
+}
+
+extension String {
+  var range: Range<String.Index> {
+    return startIndex..<endIndex
+  }
+}