Req: `-c` and `--config` to provide path to config.json

[bobpaul]

I like to make a package for this for archlinux and I have 2 goals:

• the installed path should be immutable with a config file in /etc
• a systemd template making it easier to run multiple bridges on the same server (each instance will have its own config, registration, and hangups token). Eg, an instance would launch via matrix-puppet-hangouts@FOO.service and point to configs/tokens specific for the FOO user.

To achieve these goals without a lot of weirdness in my package, I need the config path to come from the command line (it can default to ./config.json if the option isn't provided). matrix-appservice-irc has a config provided by the commandline, but I'm not a strong javascript developer and it's not clear to me how this is enabled.

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Ideally, I'd also have a -t, --token argument to provide the path to the refresh token rather than using ~/.cache/hangups/refresh_token.txt. But I can set HOME in the systemd service to move that.

[bobpaul]

Looks like I'll need to move the room-store.db and user-store.db, too.