Add async python client for Delta Chat core JSON-RPC

deltachat-rpc-client/README.md

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+# Delta Chat RPC python client
+
+RPC client connects to standalone Delta Chat RPC server `deltachat-rpc-server`
+and provides asynchronous interface to it.
+
+## Getting started
+
+To use Delta Chat RPC client, first build a `deltachat-rpc-server` with `cargo build -p deltachat-rpc-server`.
+Install it anywhere in your `PATH`.
+
+## Testing
+
+1. Build `deltachat-rpc-server` with `cargo build -p deltachat-rpc-server`.
+2. Run `tox`.
+
+Additional arguments to `tox` are passed to pytest, e.g. `tox -- -s` does not capture test output.
+
+## Using in REPL
+
+It is recommended to use IPython, because it supports using `await` directly
+from the REPL.
+
+```
+PATH="../target/debug:$PATH" ipython
+...
+In  [1]: from deltachat_rpc_client import *
+In  [2]: dc = Deltachat(await start_rpc_server())
+In  [3]: await dc.get_all_accounts()
+Out [3]: []
+In  [4]: alice = await dc.add_account()
+In  [5]: (await alice.get_info())["journal_mode"]
+Out [5]: 'wal'
+```