Bulk insert enhancements

[vadimi]

I noticed that lib/pq started to support COPY FROM STDIN. Does it make sense to rewrite BulkInsert method to use this technique for postgres (maybe by making it a part of dialect)? It is so much faster to import large amounts of data using COPY FROM STDIN.

[coocood]

I don't know this feature, and I don't know postgres well, If you can implement it and make a pull request, I will merge it.