upgrade adventureworks provenance from MS source

[smithjd]

1. Derive a Postgres restore image along the lines of https://github.com/smithjd/sql-pet/blob/master/book-src/adventureworks.sql.
2. decide whether to store the image in sql-pet or sqlpetr repositories
3. rewrite sp_postgresql_functions.R so that the image is restored to postegres from github without requiring that the whole repo be downloaded. (Not sure about this...)

[znmeb]

This is needed to clean up section 4.4 in the book!

[znmeb]

Reference Wikipedia https://en.wikipedia.org/wiki/PostgreSQL#Release_history ... PostgreSQL 9,4 goes end-of-life on February 13, 2020, but 9.5 will be supported till February 11, 2021. So we should use 9.5 instead of 9.6 to maximize the number of versions we can restore to.