In general only `-sys` crates should depend on other `-sys`
crates. IOW for us, `ostree-sys` depends on `glib-sys`.
By using the re-export, we avoid needing to keep a version lock
between `glib` and `glib-sys` in our main crate. And similar
is true of our higher level reverse dependencies (e.g. `ostree-rs-ext`).
Also weaken our dependency to `0.14` as that's clearer.
An intimidating spam of compiler errors at the start, but the
biggest was handling the new convention of `ostree_sys::` => `ffi::`.
This will require a semver bump of course.
Colin Walters
Felix Krull