Don't use sys.path[0] for storing the config and log files

[MaeIsBad]

RIght now jwt_tool uses sys.path[0] to store the config and the log files(https://github.com/ticarpi/jwt_tool/blob/master/jwt_tool.py#L1882) which makes it impossible to package it, and makes it annoying to share a single install between multiple projects. It would be nice to have it configurable via a CLI flag, have it use the CWD or use an envvar

[MaeIsBad]

Arguably it may be better to put the config in XDG_CONFIG_PATH but this was quicker to make a commit for :^