feat: set colorize default if output_unit is a terminal

Otherwise, if output_unit is redirected to a file, turn of colorization

src/veggies/command_line_m.f90

@@ -41,7 +41,7 @@ function get_options() result(options)
         integer :: iostat
         integer :: num_arguments
 
-        options%colorize_ = .true.
+        options%colorize_ = isatty(output_unit)
         options%quiet_ = .false.
         options%verbose_ = .false.
         options%filter_tests_ = .false.