makefile.kak: Refine regex for target
makefile.kak: Refine regex for target

Multiple targets and the target separators ':', '::' and '!' are now
supported.

danr/kakoune,jkonecny12/kakoune,occivink/kakoune,jkonecny12/kakoune,danr/kakoune,alexherbo2/kakoune,casimir/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,danr/kakoune,mawww/kakoune,lenormf/kakoune,occivink/kakoune,lenormf/kakoune,mawww/kakoune,mawww/kakoune,casimir/kakoune,occivink/kakoune,danr/kakoune,casimir/kakoune,Somasis/kakoune,Somasis/kakoune,jkonecny12/kakoune,lenormf/kakoune,Somasis/kakoune,mawww/kakoune,jkonecny12/kakoune,casimir/kakoune,lenormf/kakoune,Somasis/kakoune,occivink/kakoune