doc: miscellaneous touch-ups to documentation strings * debug.txi: Correct line number for debug example. * func.txi: Correct directory structure of functions shipped with Octave distribution. * edit.m: Eliminate reference to editor used by bug_report. * fzero.m: Add inline function to list of possible inputs. * fplot.m: Add comma to break list of possible inputs. * qqplot.m: Correct example so that it runs under current Octave distributions. * assert.m: Add seealso reference to fail. * fail.m: Add seealso reference to assert. Add additional calling forms of function. * load-path.cc (addpath): Don't use @samp which created double double quotes around option. * ov-fcn-inline.cc (vectorize): Add example usage. * variables.cc (exist): Add seealso link to file_in_loadpath.