Consider adding more advanced select functionality in session 3

[jayware9]

https://github.com/DataScienceScotland/intro_to_r/blob/8a8e5bd0dbf7db188065fcceb5e45110567f5ffa/session1/intro_to_r_training.Rmd#L795

We could maybe expand to include other ways of using select and rename:

• selecting name columns
• using select to rename
• some of the select helpers e.g. starts_with(), ends_with(), contains(), everything()