Windows does not support RPATH and only searches for DLLs in a small
number of predetermined paths by default, with one of them being the
directory from which the application loaded.
Installing both executables and DLLs to `bin/` by default helps ensure
that the executable can find any DLL artifacts it has linked to.
DLL import libraries are still installed to `lib/`.
These defaults match CMake's behavior.
e8f28cda9e