release python client

[jordens]

To properly pin protocol versions in downstream projects.

• release the current client (e.g. as of 22feaa7) as 0.6.3 and migrate the downstream users
• release the new client together with and as 0.7.0
• keep python client releases in semver-sync from then on

quartiq/stabilizer#661
quartiq/booster#272
quartiq/thermostat-eem#86
thermostat-mqtt
stabilizer-fls