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/statistics/base/center.m
+++ b/scripts/statistics/base/center.m
@@ -75,7 +75,7 @@
 %!assert (center (magic (3)), [3,-4,1;-2,0,2;-1,4,-3])
 %!assert (center ([1 2 3; 6 5 4], 2), [-1 0 1; 1 0 -1])
 
-%% Test input validation
+## Test input validation
 %!error center ()
 %!error center (1, 2, 3)
 %!error center (1, ones (2,2))