0.2.3 (09.12.2013)

* changed default added in 0.2.2 for generated urls to use https rather than http. fixes #2
* allow creating write-once files, by setting replace=False on upload. fixes #1
* override Storage.get_available_name to stop creating extra files when you intended to replace existing file.
* by default will now replace existing files rather than creating a new file with suffix
* tidy up duplicate code in shortcuts
* reduce the default expire period to 30 seconds