doc: Add seealso links between input, yes_or_no, kbhit. * libinterp/interpfcn/input.cc(Finput): Add seealso link to yes_or_no, kbhit. Add return argument to function documenation. * libinterp/interpfcn/input.cc(Fyes_or_no): Add seealso link to input. Redo docstring to make it more modern. * libinterp/interpfcn/sysdep.cc(kbhit): Add seealso link to input. Add second calling form of kbhit to documentation.

gnulib-hg = gnulib-hg