Add upanddowns function(s) to dfeR

## Is your feature request related to a problem? Please describe.
We don't currently have anything in dfeR which helps with describing changes/increases/decreases when writing commentary.

## Describe the solution you'd like
We could add to dfeR to include functions similar to in the upanddowns package DfT have: https://github.com/department-for-transport-public/upsanddowns

These sort of functions are used within the EduStats tool and are created there. It could be worth checking what functions are used in EduStats and whether we could use some of that code. EduStats could then potentially use dfeR for these instead of creating the functions within that project.