Add named shared memory segment containing listen address

[fredemmott]

For example:

struct YourSHM {
  uint64_t structVersion { 1 };
  uint64_t serverPid;
  uint64_t addressLength;
  wchar_t address[MAX_PATH];
};

Either using wchar's with Windows wide encoding (which isn't quite UTF16), or explicitly-UTF8 chars (not the system code page).

As for the name, I'd suggest something like aviinl.github.io/bms-kneeboard-server/SHM/1, increasing:

• the version in the SHM path every time there is a backwards-incompatible change (e.g. removing, changing, or reodering an existing member)
• the version in the SHM struct every time there is a backwards-compatible change (e.g. appending a member)

This would allow:

• an OpenKneeboard tab type to automatically detect it on any port
• bms-kneeboard-server to do the "listen on port 0, then figure out where I'm actually listening" trick to avoid port conflicts, without needing the user to reconfigure OpenKneeboard itself

The advantages of this over a file are:

• handles elevation (to an extent)
• cleanly handles process termination

[fredemmott]

A potential improvement would be to put these under OpenKneeboard/Plugins/ under a standardized format rather than per-app, and add a list in the registry.