Generic safety cleanup (#22)

* create checksum system for versioning
* minor changes to CI
* dart ffi cleanup
* update checksums

impls/monero.dart/ffigen_monero.yaml

@@ -3,7 +3,7 @@ description: monero_c bindings
 output: 'lib/src/generated_bindings_monero.g.dart'
 headers:
   entry-points:
-    - 'monero_wallet2_api_c.h'
+    - '../../monero_libwallet2_api_c/src/main/cpp/wallet2_api_c.h'
 
 exclude-all-by-default: true
 functions: