Support Fleet API and Proxy

[andig]

Fix #125

TODO

• fix examples

[andig]

We‘re testing this against the proxy now.

[andig]

@bogosj our first tests are positive now. Except for the examples this would be a good time to review the changes and make a decision if you want to continue hosting the module.
In terms of api I'm not super happy with the Set*Url methods but need them to switch between fleet api directly and proxy. In addition it would also be nice to swap the client for an existing vehicle (in case vehicle was retrieved reading from fleet api but one would like to send commands to using proxy).
Also worth noting that Powerwall still seems to support the owner api/ tokens.

[bogosj]

I have no objection to continuing to keep the library as bogosj/tesla. I'm probably not going to go to the effort to update my only use of this library, so I have no vested interest in keeping it alive. Perhaps it would be best with this major breaking change to take the opportunity to re-home it?