* removes content support from iroh-sync
* adds a quick-and-dirty writable database to iroh-bytes (will be
  replaced with a better generic writable database soon)
* adds a `Downloader` to queue get requests for individual hashes from
  individual peers
* adds a `BlobStore` that combines the writable db with the downloader
* adds a `Doc` abstraction that combines an iroh-sync `Replica` with a
  `BlobStore` to download content from peers on-demand
* updates the sync repl example to plug it all together
* also adds very basic persistence to `Replica` (encode to byte string)
  and uses this in the repl example

* make the REPL in the sync example work properly with rustyline for
  editing and reading input, shell-style argument parsing and clap for
  parsing commands
* add a docs store for opening and closing docs
* add author to doc struct

uses flume channels to allow for combined sync and async usage

* start refactoring store into its own module

* implement more details

* works again

* draft fs db and integrate error handling

* fill out more of the implemenation

* lifetime sadness

* self referential fight: Rust 0 - Dig 1

* basic tests and range fixes

* introduce Store trait and update tests to test against both impls

* implement remove

* integrate new storage into the example

* implement iterators

* fixes and more tests

* clippy and deny cleanup

* removed the `Doc`, `DocStore`, `BlobStore` abstractions, they were not
  the right way for now
* Introduce `SyncEngine` that combines the gossip `LiveSync` with
  on_insert callbacks to download content, to replace the functionality
  from the above-mentioned abstractions
* Rename `iroh_sync::get_replica` to `iroh_sync::open_replica` and
  expect them to be singletons per namespace
* Various other minor fixes and improvements to logging

wip: more methods

wip: integration of iroh-sync in iroh

changes after rebase

continue integration of iroh-sync in iroh node

* removed the `Doc`, `DocStore`, `BlobStore` abstractions, they were not
  the right way for now
* Introduce `SyncEngine` that combines the gossip `LiveSync` with
  on_insert callbacks to download content, to replace the functionality
  from the above-mentioned abstractions
* Add RPC handlers on the `SyncEngine` for the most important operations
* Introduce `iroh::client::Iroh`, a wrapper around the RPC client, and
  `iroh::client::Doc`, a wrapper around RPC client plus document id
* Use the new client structs in the CLI
* Rename `iroh_sync::get_replica` to `iroh_sync::open_replica` and
  expect them to be singletons per namespace
* Various other minor fixes and improvements to logging