Add support for proper lambdas (#48)

* Add support for proper lambdas

* Get rid of recursion

Remove renderSectionLambda as I can use renderUnescapedLambda for that.

Sources/Mustache/Template+FileSystem.swift

@@ -24,7 +24,9 @@ extension MustacheTemplate {
         let fs = FileManager()
         guard let data = fs.contents(atPath: filename) else { return nil }
         let string = String(decoding: data, as: Unicode.UTF8.self)
-        self.tokens = try Self.parse(string)
+        let template = try Self.parse(string)
+        self.tokens = template.tokens
+        self.text = string
         self.filename = filename
     }
 }