Bump program version to 0.92.1

* I planned to separate plugins from main program so that
  we can update them independently. That's why plugin version
  is different from that of main program.
  But the plugins are still bundled with main program, we have to
  update version number when any single part gets updated...

Bump main & plugin ver to 0.92

Release note:

This release contains:

* A minimal GBK -> UTF-8 converter, which can be used to reduce
  binary size while keeping server messages readable.
* A proprietary header generator for IPv4 information.
* Manpage and systemd service template. Ready for packaging.

Thanks to all contributors!

Footnote:

* I wish I had named previous tag 0.9.1

pid_lock: Fix missing include under Linux & inconsistent whitespace

* And restore default config.mk for Linux
* Should have noticed before pushing...

Milestone: It works!

* Tested in real environment and it passes the authentication! The fields are correctly stitched together.
* The authentication server here does not check ANY field. Even if I remove `rjv3_append_common_fields` (only add the 62-byte header) it still passes the authentication.