Add StreamTransfer

This class manages an asynchronous operation to read from one stream
and write to another. This class is only available in .NET 4.5.
Improve EmbeddedResourceReader

* Fix StringTree

* Make BidirectionalDictionary enumerable

* Add Indent to functions

* Rename DefaultNameTranscoder to TranslatingNameTranscoder, and fix
  its algorithm for converting from a path to a resource name.

* Create a DictionaryNameTranscoder, which can be loaded up with
  explicit mappings.