Save a formula or any string which starts with "=" as a string using the cells-based interface

[miron1512]

Hi @theoephraim,
There is currently no way to save a formula or any string which starts with "=" as a string using the cells-based interface.
I think that if we explicitly use cell.stringValue, we already know that we want to save the value as string, regardless of whether it's a formula or any string which starts with "=". So, we don't need to throw an error here:

I created a small PR to fix this: #643

[theoephraim]

yeah I think this is right. I swore I had already made it work this way, but might have gotten lost while doing some other bigger refactoring. Will get this merged in with some tests shortly.