Add <C-d> and <C-u> for scroll down/up half a page
Add <C-d> and <C-u> for scroll down/up half a page

Fixes #606

lenormf/kakoune,casimir/kakoune,ekie/kakoune,mawww/kakoune,jkonecny12/kakoune,ekie/kakoune,ekie/kakoune,jjthrash/kakoune,occivink/kakoune,flavius/kakoune,alexherbo2/kakoune,danr/kakoune,flavius/kakoune,lenormf/kakoune,mawww/kakoune,jkonecny12/kakoune,casimir/kakoune,jjthrash/kakoune,alexherbo2/kakoune,flavius/kakoune,lenormf/kakoune,flavius/kakoune,mawww/kakoune,jjthrash/kakoune,Somasis/kakoune,jkonecny12/kakoune,ekie/kakoune,jkonecny12/kakoune,jjthrash/kakoune,mawww/kakoune,danr/kakoune,occivink/kakoune,Somasis/kakoune,occivink/kakoune,danr/kakoune,Somasis/kakoune,casimir/kakoune,casimir/kakoune,Somasis/kakoune,alexherbo2/kakoune,occivink/kakoune,lenormf/kakoune,danr/kakoune,alexherbo2/kakoune