Nice!
I just hacked 

```
stm32-metapac = { version = "16.0.0", features = ["stm32f303cb"] }
stm32f3xx-hal = { version = "0.10.0", features = ["ld", "rt", "stm32f303xb"] }
```

in my Cargo.toml file, and seem to be able to use the metapac in parallel to stm32-rs :)