Added conversion of hostname to IP

[gollumben]

Dear Orca,

thank you very much for this neat piece of code!

I added the support to connect to influxdb using the hostname instead of the IP address.

Cheers,
Ben

[manubrulo]

Please accept this pull request since I had to add it manually once I cloned the repo without knowing that this was already solved but not added.

[orca-zhang]

Dear Ben,

Thanks to your contribution.

The feature helps when put in a hostname instead of IP address.

But inet_ntoa is not thread-safe, inet_ntop maybe better.

And I think new solution should be found to instead std::exit when failed to translate hostname to IP address.

Best Regards,
Orca