Move cargo bins to examples/, and fix the cargo building.

Make sure ./configure is run when building.
DEPS_DIR is provided by cargo so the linker can see object archives. Put the gtk_glue there, so it can be seen when lib is built as a dependency, or when running tests.

Examples go in ./examples  and can be built with `cargo test'. This stops their dependency on 3.12 breaking the build. They can also be built separately by using cargo with ./examples as the working directory.