Support multiple goal patterns in verifier

[nbeloglazov]

Verifier provides flag --goal_regex that allows for custom goal regexes. It works well for single languages, not so well for 2+ languages that have different style of comments. For example here is a regex that supports both //- goal and <!-- goal --> comments: \\s*(?:\\/\\/-|<!--)([^>]*)(?:-->)?$. It's pretty unreadable.

It would be good if we could pass multiple --goal_regex values and verifier will try them all. Or some other approach for providing 2+ different goal patterns.