Separate option --multiline-dotall and --multiline

[feng-qi]

Using option --multiline doesn't necessarily mean the user also wants
--multiline-dotall. The user may be certain about the number of new lines
involved. For example, with this code snippet:

    if (level == 2U) {
        parent_irq = irq_parent_level_2(irq);
        table_idx = parent_offset + irq_from_level_2(irq);
    }
#ifdef CONFIG_3RD_LEVEL_INTERRUPTS
    else if (level == 3U) {
        parent_irq = irq_parent_level_3(irq);
        table_idx = parent_offset + irq_from_level_3(irq);
    }

If I want to search all the #ifdef followed by a else statement, I can use regex
#ifdef.*\n.*else. If --multiline-dotall is used, this regex will match more
lines than I expected.

[feng-qi]

Besides, one can use the dot all modifier, which looks like (?s), to change the dot's behavior if --multiline-dotall is not available. https://til.hashrocket.com/posts/9zneks2cbv-multiline-matches-with-ripgrep-rg

[coveralls]

Coverage remained the same at 80.775% when pulling e3af9b3 on feng-qi:master into 0fa6d33 on dajva:master.