Configurable encoding of template files, closing #65. * The `XMLParser` constructor now accepts an optional encoding parameter. * The `MarkupTemplate` and `TextTemplate` class also get an encoding parameter in their initializers. * A `default_encoding` can be specified when creating a `TemplateLoader` instance, but the encoding can also be specified explicitly when calling the `load()` method. * Encodings specified using an XML declaration in templates and XML files are now honored (as long as Expat supports them, that is, and it doesn't support many).