fontspec options cannot contain fragile contents

[wspr]

This isn't usually a problem, but in many places in the fontspec code the user-passed options are fully expanded before being passed onto \setkeys and so on.

This is a problem for things like HyphenChar=\%, which should work but doesn't because the \% is attempted to be expanded before its time. On the other hand, I would like the user to be able to pass in macros as arguments, so maybe an f type expansion would be the more useful.

In any case, this part of the code logic should be revisited.