BUG: Some sas7bdat files with many columns are not parseable by read_sas
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

The reason is that column definitions may be split up into different pages.
Allow column information to be parsed from different pages
and add a test for it.
