Display a number, optimized for HTML output.
$number is the correct number, $altnum may be used to display user input
-D dev mode, will display number(s) as placeholder
-f process fractions
-i input (form mode)
-I input, use number as default, add as placeholder
-l margins left
-L margins left
-m margins left & right
-M margins left & right
-r margins right
-R margins right
ONO::Lib::Math::HTML->display_number( $number, $switches, $id, $altnum );
returns: $HTML