Goal
make regular expression pattern stricter so that we won't accidentally match things we don't need

Description
In commitizen/cz/conventional_commits/conventional_commits.py#L33 on command-changelog branch, I use named capture group so that we could use a stricter regular expression like .*\n\nBREAKING CHANGE. The benefit of it is that we don't have to break the whole commit message into lines like commitizem/bump.py#L31. It can also avoid bump or generate changelog based on commit message like fix --- it does not follow the rule but still match the pattern.
Another thought on this topic is that we probably merge the bump_map and bump_pattern into one some data class to store name(e.g., break), pattern(e.g., .*\n\nBREAKING CHANGE), behavior(e.g., PATCH).