Added backups for single file saving

This release adds backups for single file saving. Data folders are still on their own with whatever TiddlyWiki has for them. The old version of a single file put request will be gzipped (to save space) and stored in the specified directory, which is undefined by default. If no directory is specified, it will not create a backup. The file is named with the server request path and the modified time of the original file.