Snd 17.7:

Mike Scholz provided changes for Ruby 2.5.

s7: changed various "object" names to "c_object" in s7.h ("object" was ambiguous)
    c-pointers can participate in the generic function stuff
    gtkex.scm
    json.scm (aimed at the Language Server Protocol, eventually in emacs perhaps)

checked: gtk 3.91.2, sbcl 1.3.21

Thanks!: Kjetil Mattheussen, Mike Scholz
