CLI Check for Updates

[gfiumara]

Many will download our pre-built binary. We should provide them a mechanism to ensure they have the latest version. Options to check for updates might include checking for new git tags, changes in version.cpp.in, etc.

This should be:

• completely optional
• opt-in (ask the user if they want to check before network code loaded)
• be able to be disabled
• be able to be compiled out (some high-security environments might not want any socket code)
• (hopefully) not introduce another library dependency