The API of Automerge::generate_sync_message requires that the user keep
track of in flight messages themselves if they want to avoid sending
duplicate messages. To avoid this add a flag to `automerge::sync::State`
to track if there are any in flight messages and return `None` from
`generate_sync_message` if there are.
Generating patches to text objects (a la the edit-trace benchmark) was
very slow due to appending to the back of a Vec. Use the SequenceTree
(effectively a B-tree) instead so as to speed up sequence patch
generation.
The assert_doc and assert_obj macros in automerge/tests::helpers are
useful for writing tests for any application working with automerge
documents. Typically however, you only want these utilities in tests so
rather than packaging them in the main `automerge` crate move them to a
new crate (in the spirit of `tokio_test`)
After some discussion with PVH I realise that the repo structure in the
last reorg was very rust-centric. In an attempt to put each language on
a level footing move the rust code and project files into ./rust
