Add I2C `software_reset` method.

[reitermarkus]

Add method for software reset via the “General Call” address.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @ryankurte (or someone else) soon.

Please see the contribution instructions for more information.

[eldruin]

We discussed this in the meeting today and decided against merging it due to a number of reasons:

• It does not seem anybody would need anything else than the default implementation, so it would not build an abstraction that implementations later define, like with the rest of traits.
• It is trivial to do in user code if needed: bus.write(0x0, &[0x06]).
• It has potential for unintended foreign device resets.
• Support for I2C General Call Reset command is rare.

Nevertheless, thank you very much for the proposal!