Changes:
* Makefile adaptations should help building and running this for some. Thanks for the pull requests.
* Fixed some bugs regarding carbons and sending messages to yourself, also added NULL checks so that it plays nicer with other plugins which might set the message to NULL
* Update submodules and their dependencies, most importantly libsignal-protocol-c to 2.3.2
* Add plugin preferences prototype: Single option is logging verbosity on the debug log
In German, an Axolotl is a type of Lurch, which simply means
'amphibian'. This plugin brings Axolotl, by now renamed to double
ratchet, to libpurple applications such as Pidgin by implementing
the XEP-0384: OMEMO Encryption.
