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/set/powerset.m
+++ b/scripts/set/powerset.m
@@ -100,7 +100,7 @@
 
 %!assert (powerset([]), {});  # always return a cell array
 
-%% Test input validation
+## Test input validation
 %!error powerset ()
 %!error powerset (1,2,3)
 %!error <expecting second argument to be "rows"> powerset (1, "cols")