The refactored plugin is `tiddlyweb2` for the moment. The idea is to be
able to use the same syncer with a different adaptor for syncing
changes to the local file system.
Lots of changes:
* Make the built-in server support recipes and bags, albeit there's
just one of each, called "default"
* Correctly parse returned Etag to get bag of freshly PUT tiddlers
* URI encoding for tiddler titles, so that tiddlers with slashes and so
on work OK
