Support multiline chatop pattern matching

[laserlemon]

The test added is actually a decent example of how multiline chatop matching could be useful. My intended use is a command to complement a suite of existing commands that manage a list of terms. The new command would allow the entire dictionary of terms to be replaced in one fell swoop. For example:

prefix fruits replace

apple
banana
lemon

[nerual]

Also coming here to give this a friendly nudge, as this would greatly help our chatop accept a multi-line backtrace!