feat(blog): Support custom font size for readers

[jackblk]

We should let user to increase/decrease the font size or spacing in FE & save the setting to local storage/cookies.

Perhaps also letting repo owner to set default setting in their repo config?

[thien-do]

thanks @jackblk !

Perhaps also letting repo owner to set default setting in their repo config?

Yes. For preferences/configurations, we'd prefer them to be in both places:

• a default defined by author via the memos.json config
• while readers can always set it again at the blog (localStorage)