Support loading a template from disk

Closes #4

README.md

@@ -22,11 +22,11 @@ let context = Context(dictionary: [
     ]
 ])
 
-let template = Template(path:"template.stencil")
+let template = Template(named: "template.stencil")
 let result = template.render(context)
 
 if let error = result.error {
-    println("There was a syntax error parsing your template (\(error)).")
+    println("There was an error rendering your template (\(error)).")
 }
 
 println("\(result.string)")

Stencil/Template.swift

@@ -8,9 +8,31 @@
 
 import Foundation
 
-public struct Template {
+public class Template {
     let nodes:[Node]
 
+    public convenience init(named:String) {
+        self.init(named:named, inBundle:nil)
+    }
+
+    public convenience init(named:String, inBundle bundle:NSBundle?) {
+        var url:NSURL?
+
+        if let bundle = bundle {
+            url = bundle.URLForResource(named, withExtension: nil)
+        } else {
+            url = NSBundle.mainBundle().URLForResource(named, withExtension: nil)
+        }
+
+        self.init(URL:url!)
+    }
+
+    public convenience init(URL:NSURL) {
+        var error:NSError?
+        let templateString = NSString.stringWithContentsOfURL(URL, encoding: NSUTF8StringEncoding, error: &error)
+        self.init(templateString:templateString)
+    }
+
     public init(templateString:String) {
         let lexer = Lexer(templateString: templateString)
         let tokens = lexer.tokenize()