gbui 0.2.1

A packaging fix, released from 0.2.x rather than from main: the branch is
0.2 and this, and nothing else.

Fixed

• A shared build could not run its own executables on Windows. Windows has
  no rpath — a program finds a DLL beside itself or on PATH — while CMake's
  multi-config generator puts the library in build/Release/ and every
  executable in build/<dir>/Release/. The build and the link both succeed and
  the loader fails at startup, which on a machine with no desktop is a dialog
  nobody can dismiss: the process never returns and never says why. The CI job
  that builds shared and runs the tests sat for six hours before it was
  cancelled. The DLLs are copied beside each executable now, on Windows and only
  when the build is shared.
• CI grew the ceilings whose absence turned that bug into six hours:
  ctest --timeout 180, so a hung test fails with its own name, and
  timeout-minutes on the job that found it.