Review updated version of homie convention

[jalmeroth]

https://github.com/marvinroger/homie/tree/v2

[bodiroga]

Now that Homie follows a semser (semantic versioning) schema, we can start fully supporting the 2.0.1 version. That's the version that homie-esp8266 supports, so we can stay in sync with them for now and later on start supporting the 3.X branch.

What do you think?