The primary motivation for this commit was rust-lang/cargo#4189 where dropping a
`wincolor::Console` would call `CloseHandle` to close the console handle. Cargo
creates a few `Console` instances so it ended up closing stdout a little
earlier as intended!
The `GetStdHandle` function returns handles I believe aren't intended to be
closed (as there's no refcounting). I believe libstd doesn't close these
handles.
This commit also moves to calling `GetStdHandle` on demand which libstd changed
to doing so recently as well, preventing caching of stale handles that change
over time with calls to `SetStdHandle`.
