feat: reorg code, and prepare for c bindings

README.md

@@ -1,3 +1,15 @@
 # Delta Chat Rust
 
 Current commit on deltachat/deltachate-core: `12ef73c8e76185f9b78e844ea673025f56a959ab`.
+
+## Development
+
+```sh
+# run example
+$ cargo run --example simple
+# build header file
+$ cargo build -p deltachat_ffi --release
+$ cat deltachat-ffi/deltachat.h
+# run tests
+$ cargo test --all
+```