Writer mode : add a custom to define the default font family

[albreche]

Hi there, writer-mode.el hard code font family withuin face remapping.
I prefer variable font for writings, i propose to define a custom variable and some rework wthin the mode.
Here attached a first attempt. What do you think about this ?
0001-add-a-custom-family-for-writer-mode.patch

[mrzor]

Shouldn't defface be used for such a thing instead of defcustom ?

[rougier]

There's now a book mode that might be the place to propose the patch.