Remove custom Result type and throw errors

Stencil/TemplateLoader/Include.swift

@@ -1,44 +1,37 @@
 import Foundation
 import PathKit
 
-extension String : Error {
-  public var description:String {
-    return self
-  }
-}
 
-public class IncludeNode : Node {
+public class IncludeNode : NodeType {
   public let templateName:String
 
-  public class func parse(parser:TokenParser, token:Token) -> TokenParser.Result {
+  public class func parse(parser:TokenParser, token:Token) throws -> NodeType {
     let bits = token.contents.componentsSeparatedByString("\"")
 
     if bits.count != 3 {
-      return .Error(error:NodeError(token: token, message: "Tag takes one argument, the template file to be included"))
+      throw TemplateSyntaxError("'include' tag takes one argument, the template file to be included")
     }
 
-    return .Success(node:IncludeNode(templateName: bits[1]))
+    return IncludeNode(templateName: bits[1])
   }
 
   public init(templateName:String) {
     self.templateName = templateName
   }
 
-  public func render(context: Context) -> Result {
+  public func render(context: Context) throws -> String {
     if let loader =  context["loader"] as? TemplateLoader {
       if let template = loader.loadTemplate(templateName) {
-        return template.render(context)
+        return try template.render(context)
       }
 
       let paths:String = loader.paths.map { path in
         return path.description
-        }.joinWithSeparator(", ")
-      let error = "Template '\(templateName)' not found in \(paths)"
-      return .Error(error)
+      }.joinWithSeparator(", ")
+      throw TemplateSyntaxError("'\(templateName)' template not found in \(paths)")
     }
 
-    let error = "Template loader not in context"
-    return .Error(error)
+    throw TemplateSyntaxError("Template loader not in context")
   }
 }