Migrate to bson v3.0

[adrien3d]

While updating my mongo crate, I realized that bson is still in v2.15 whereas v3.0 was released 2 months ago.
It causes a breaking change in from_bson when I want to use bson v3.0 with latest mongodb 3.3
Can you please update bson?
Thanks

[abr-egn]

Because the bson types are part of the driver API, switching to bson 3.0 by default would unfortunately be a breaking change. You can opt-in to use bson 3.0 with the bson-3 feature added in mongodb 3.3.0 🙂

It does look like we forgot to add that feature to the list in the README / crate doc, I'll fix that shortly.