Add 3d book feature to homepage and single post page
Add books page
Tweak position of subscribe icons when no video
Revert to centered content
Switch from Gumroad to SendOwl
Merge branch 'new-feature/book'

* new-feature/book:
  Switch from Gumroad to SendOwl
  Revert to centered content
  Tweak position of subscribe icons when no video
  Add books page
  Add 3d book feature to homepage and single post page