instead of having a static one, as that could end up taking up a
lot of memory if your app keeps olm sessions hanging about.

As a way to dump the state of an olm session, ie. the chain indicies,
so we can debug why olm sessions break and get out of sync.

Add versions of olm_session_create_inbound and olm_session_matches_inbound which take the curve25519 identity key of the remote device we think the message is from as an additional argument

Rename axolotlpp as olm to avoid confusion with Axolotl-the-spec and Axolotl-the-OWS-libraries at moxie's request