doc/kak.1: split the synopsis for each mutually exclusive mode of operation.
doc/kak.1: split the synopsis for each mutually exclusive mode of operation.

Previously, the manpage listed every flag and parameter as optional, implying
that they could be used in any combination, which isn't true. As a trivial
example, to use Kakoune in "list sessions" mode, you *must* specify -l, and you
*must not* specify any other options. To use Kakoune in any other mode, you
*must not* specify -l.

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