Replace multiple whitespaces with single whitespace

[achwell]

If a table cell has more than one line; the excel-cell will have a lot of whitespace. It would be nice to be able to replace all that whitespace with only one space.

[alephreish]

If the table content is generated within a web-framework, there is most of the time no reliable way to control how the spaces are arranged. If white space is irrelevant to html, it should be irrelevant for the export as well.