Improvements to the time and watchdog interface

[JanekGraff]

• Add types for MicroSeconds, MilliSeconds and Seconds to time.rs and add conversions between them (the ones that don't loose precision while converting.
• Update the IwdgTimeout struct to be able to construct it from any type that implements Into<MicroSeconds> (The old parameter in Hertz can still be used since Hertz implements Into<MicroSeconds> as well)

There is probably some more interfaces that could benefit from a similar change in generic parameters to also support (Micro/Milli)Seconds instead of only Hertz. Feel free to list them here and I'll try to add/change them if i got some time