Update to latest dependencies; add an example

I switched to MIT, as per the discussion in #rust:gnome.org. Not sure if you need more formal approval from the, uh, one other contributor?

Not much in the way of extensive testing yet, but the example does fetch successfully, so at least that much works.

Couple questions/things I'm uncertain about since I haven't used gir since my Vala days:

• Had a bit of trouble with &[&str] and map, which is why part of Session is ignored. Is there something I can do to fix that?
• I didn't see a soup_init function, so the init macros in crate::rt are all no-ops. I assume that isn't correct?
• The rest of Gir.toml is copied from whizsid/soup-rs. If there's anything sub-optimal, let me know!