Hello all,

Since #863 (v1.13.0), header and footer can be exported, which I think is a great feature!
However, I found that header and footer cannot be imported from existing xlsx files.

To reproduce, create an xlsx file with any header/footer (say foo.xlsx) and execute in NodeJS:

const Excel = require('exceljs')
const wb = new Excel.Workbook()
wb.xlsx.readFile('foo.xlsx')
wb.getWorksheet(1).headerFooter

This returns just undefined, but I expect an object with properties like oddFooter.

I opened a PR for this: #1000