Search for specified delimeter to split transactions

[kudrevatykh]

We use liquibase formatted sql format for our migrations https://docs.liquibase.com/concepts/changelogs/sql-format.html
Problem occurs when we use several changes in single sql file. squawk considers that all changes in file are run in single transaction becase we use --assume-in-transaction flag.
It would be nice if squawk split migration file in several transactions by user-specified delimeter (in our case if line starts with --changeset it means that different transaction starts). Now we mandated to write each migration in separate file.

[sbdchd]

One tricky thing is the Postgres parser doesn't return AST nodes for comments so we'd have to bolt something on top for that

[kudrevatykh]

I think such splitting could be made before Postgres parser.