environment: migrate interface from physic.SenseEnv

[maruel]

• environment.SenseWeather replaces physic.SenseEnv in v4.
• Use Weather instead of Env. This is more precise.
• Use SenseWeather() instead of Sense(). The rationale for the rename is that we will add new SenseXX() functions, and a single device could sense multiple things (environment, orientation, etc) on the same Go object. Having all interfaces uses the generic verb 'Sense()' would cause conflict.
• Add examples but do not implement it yet.
• Make SenseWeatherContinous blocking (synchronous) and require a context. This is part of the larger context based operation in v4.

Package physic wasn't the right place to host this interface. Other interfaces (like orientation) can be added to package environment.

No behavior change, only new interfaces.

[maruel]

I'm not a fan of environment.SenseWeather.SenseWeather(). Better naming ideas are appreciated.

I did the implementation of all the current sensors, including SenseWeatherContinuous(), but I want to nail down the API first.

[maruel]

This needs to be redone, I'll open a separate CL.