Ed25519 private keys, it turns out, have 64 bytes, not 32.

We were previously generating only 32 bytes (which is all that is required to
generate the public key), and then using the public key as the upper 32 bytes
when generating the per-message session key. This meant that everything
appeared to work, but the security of the private key was severely compromised.

By way of fixes:

 * Use the correct algorithm for generating the Ed25519 private key, and store
   all 512 bits of it.

 * Update the account pickle format and refuse to load the old format (since we
   should consider it compromised).

 * Bump the library version, and add a function to retrieve the library
   version, so that applications can verify that they are linked against a
   fixed version of the library.

 * Remove the curve25519_{sign, verify} functions which were unused and of
   dubious quality.

I want to use test_olm.sh on jenkins, which lacks jq. Hence, add support to
olm.main to get id and one-time keys individually.

We need to be able to inspect an outbound session so that we can tell our peer
how to set up an inbound session.

Split the python wrappers into separate modules

switch from /usr/bin/python to /usr/bin/env python. this doesn't help folks whose python path points at python3 (e.g. Arch linux) though, but I see no choice than they have to change the shebangs, as we do on Synapse.  For instance, OSX doesn't have a python2 symlink, otherwise we'd use /usr/bin/env python2 shebang.

Call the right c function from Session.matches_inbound. It was calling create_inbound_session rather than matches_inbound_session