GitLab

It should depend on the highest API version we support.

All dependencies now also are compiled with the same version feature as
the crate itself, allowing for more caching of build results by cargo.

These only work with gitlab.com and not other instances.

This is also getting us rid of bitflags.

The ABI tests are not all succeeding yet.

gst_flow_combiner_ref/unref were introduced in gstreamer-1.12.1 but they
inherit the `since version` declared for `GstFlowCombiner` which is 1.4.

Fixes https://github.com/sdroege/gstreamer-sys/pull/5

This will later become 0.3.0, 0.2 development happens in the 0.2 branch

Fixes https://github.com/sdroege/gstreamer-sys/pull/1

Otherwise development against GIT versions of glib-rs are not possible
due to linking in different versions of the same crate.

This now generates untruncated structs for almost everything.