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/regexptranslate.m
+++ b/scripts/strings/regexptranslate.m
@@ -78,7 +78,7 @@
 %!assert (regexptranslate ("wildcard", "/a*b?c."), "/a.*b.c\\.")
 %!assert (regexptranslate ("escape", '$.?[abc]'), '\$\.\?\[abc\]')
 
-%% Test input validation
+## Test input validation
 %!error <Invalid call to regexptranslate> regexptranslate ()
 %!error <Invalid call to regexptranslate> regexptranslate ("wildcard")
 %!error <Invalid call to regexptranslate> regexptranslate ("a", "b", "c")