Version checking

Starting from version 2.0.9 , ProxySQL has enabled automatic version checking.
During startup it will automatically connect to ProxySQL website and write in the error log (or standard error) the latest version of ProxySQL available.

No further action is performed.

The check is implemented in the background (thus not blocking during startup) and it times out after 10 seconds.
That means it works fine also if running on a network without Internet access.

It is possible to disable version checking starting proxysql with the command line option --no-version-check.