maint: Clean up m-files to follow Octave coding conventions. Try to trim long lines to < 80 chars. Use '##' for single line comments. Use '(...)' around tests for if/elseif/switch/while. Abut cell indexing operator '{' next to variable. Abut array indexing operator '(' next to variable. Use space between negation operator '!' and following expression. Use two newlines between endfunction and start of %!test or %!demo code. Remove unnecessary parens grouping between short-circuit operators. Remove stray extra spaces (typos) between variables and assignment operators. Remove stray extra spaces from ends of lines.

--- a/scripts/strings/cstrcat.m
+++ b/scripts/strings/cstrcat.m
@@ -63,7 +63,7 @@
 %!assert (cstrcat ("foo", "bar"), "foobar")
 %!assert (cstrcat (["a"; "bb"], ["foo"; "bar"]), ["a foo"; "bbbar"])
 
-%% Test input validation
+## Test input validation
 %!error cstrcat ()
 %!error cstrcat (1, 2)