memory leaks in the implementation.

https://matrix.org/docs/spec/client_server/unstable.html#key-export-format

Currently, importing does not work.  Do not use this commit
if you intend to keep import/export working.  I also have not yet
cleaned up the code, so there might be some nasties that have
not been discovered.

This at least partially addresses #3.  I have a feeling that
additional updates will be needed at some point, but this
fixes the issue where mtxclient would throw an exception for
unrecognized event id formats, which caused nheko to crash.

That's what the README suggests and - more importantly - the cmake
config file works with.
Also use angle brackets instead of quotation marks in two cases.

- Remove the one time key that is used to create an inbound OlmSession.

Add a temporary fix for travis-ci with regard to wrongly exported include directories.