OpenVPN plugin examples.

Examples provided:

simple.c -- using the --auth-user-pass-verify callback, verify
            that the username/password is "foo"/"bar".

To build:

  ./build simple (Linux/BSD/etc.)
  ./winbuild simple (MinGW on Windows)

To use in OpenVPN, add to config file:

  plugin simple.so (Linux/BSD/etc.)
  plugin simple.dll (MinGW on Windows)