Implement HardwareVersionDetector

[dbrgn]

A simple hardware version detector on PA12 / PB4 / PB5.

Current output via serial:

Should we keep the hardware version as an integer, or should I map it to an enum (where 0 would correspond to V2_0 and others would correspond to Unknown(u8))?

[rnestler]

Should we keep the hardware version as an integer, or should I map it to an enum (where 0 would correspond to V2_0 and others would correspond to Unknown(u8))?

The enum would probably make the handling more readable:

match hw_version {
    HardwareVersion::V2_0 => {},
    HardwareVersion::Unsupported(version) => { panic!("Unsupported hardware version {}",  version); }
}

[dbrgn]

Updated, I confirmed that it works!