buffered I/O

the test code is much faster but don't really need to fetch event on the cloud (as only the latest event are pulled and they still are in the buffer)
there's a bit of refactoring with two new classes (LocalCache and BufferedBlobIO) but it isn't finished
also, still no unit tests (who needs tests anyway?)
Merge branch 'master' of https://github.com/Evernest/Evernest