Implement explicit NO_COLOR env support

Further options to achieve the same:
- Use --no-color command line argument (since 2010-02-25, 62a3167)
- Select "Monochrome" color scheme from Setup screen (f5f29ce)

Author: BenBE

CommandLine.c

@@ -119,6 +119,12 @@ static CommandLineStatus parseArguments(int argc, char** argv, CommandLineSettin
       .hideFunctionBar = false,
    };
 
+   {
+      const char* no_color = getenv("NO_COLOR");
+      if (no_color && no_color[0] != '\0')
+         flags->useColors = false;
+   }
+
    const struct option long_opts[] =
    {
       {"help",       no_argument,         0, 'h'},