Make maximum line count a setting

[dgw]

It's good to have a sane default (and once 3.0 support is handled I'll look at tweaking the default limit). But some bots have different use cases than others, and might prefer to avoid notices in favor of slightly more channel spam.

One way to do this would be to behave the way Rizon's Internets bot does. See the example config

[dgw]

Adding to the v0.4.0 milestone because it'll be good to have a somewhat major enhancement like this go with the bump in library version compatibility.