section header case checks

[robjhyndman]

From author of 2024-30:

2) The check says most of the section headings are not in sentence case.  There are two reasons.  Firstly I call the plots UpAndDown plots so that the mix of upper and lower case letters reflects the name and the plot form itself.  Secondly, there are three sections on applications with these headings: 
Visualising changes in the UK Consumer Price Index
Visualising population changes in Northern Ireland
Visualising brand share change in German car sales
Surely the last three should be allowed?  The packages uses the name UpAndDown plot in its documentation without objection from CRAN and I would hope the name could be kept.

[dicook]

This is impossible to check perfectly. Some of the checks should just report the potential issues, and let the author decide whether a change is needed.