[rest] Adds classes for file upload.
Merge branch 'master' of https://github.com/skeinlib/skein

Conflicts:
	skein-rest/src/skein/rest/client/extras/Uploader.as
	skein-rest/src/skein/rest/client/extras/upload/UploadFactory.as
	skein-rest/src/skein/rest/client/extras/upload/UploadWriter.as
	skein-rest/src/skein/rest/client/impl/extras/DownloaderHandler.as
	skein-rest/src/skein/rest/client/impl/extras/UploaderHandler.as