Bump version
[CLI] allow to pass the current store as optional argument

By default, still consider ./.irmin as the current store.
Add some spaces in IrminJSON.json_of_src
Tentative implementation of IrminJSON.of_stream

This converts a stream of strings into a stream of JSON objects. It compiles, but it is untested.
Slightly modify the signature of S.watch
Dummy implementation of S.watch

Not sure it's the best way to hook it up but that's ok for now on.

Would be probably better to add it in IrminStore.M and let the backends implement it themself (using inotify for the FS backend for instance).
Implement S.watch in the HTTP server.
Implement S.watch in the CRUD clients
Implement S.watch in the CLI

Note 1: you'll need to pass through the HTTP server to have working notifications (i.e 'irmin watch <path> -r <server-adress>) which is not very ideal but good enough for now on.

Note 2: the unmarshalling of events seems broken but at least events are sent/received.