Option to just spit out a `.sql` file instead of actually doing updates on DB?

[pathikrit]

This would be useful when we want to simply generate the .sql file and do the upgrade elsewhere or maybe check-in the schema transformation file and use it in tests repeatedly.

[dimitri]

pgloader already has code to output in the COPY format, and we could add CSV quite easily too. I've also been asked in the past about SQLite format, see #122.

Just adding it to the wishlist so that any contributor may feel free to work on non PostgreSQL output support!