Update deps, add concache dep
Ignoring the build dir
Introduces con_cache to keep track of output files

This is in preparation for being able to output to different
    files depending on the received message's payload.

TODOs:
* Be able to configure the timeout of a file (ie how long of
    inactivity before it is closed). See outputter.ex:23
* Improve get_filename to be smarter, outputter.ex:92