Add command-line options to force-enable/disable color

`-forcecolor` will force color to be on. `-nocolor` will force color to
be off.

And just because I'm a nice person, I've also added British versions of
those flags. As a treat.

desktop_version/src/Vlogging.c

@@ -47,6 +47,11 @@ void vlog_init(void)
     }
 }
 
+void vlog_toggle_color(const int enable_color)
+{
+    color_enabled = enable_color;
+}
+
 int vlog_info(const char* text, ...)
 {
     va_list list;

desktop_version/src/Vlogging.h

@@ -8,6 +8,8 @@ extern "C"
 
 void vlog_init(void);
 
+void vlog_toggle_color(int enable_color);
+
 int vlog_info(const char* text, ...);
 
 int vlog_warn(const char* text, ...);

desktop_version/src/main.cpp

@@ -432,6 +432,14 @@ int main(int argc, char *argv[])
                 playassets = "levels/" + std::string(argv[i]) + ".vvvvvv";
             })
         }
+        else if (ARG("-forcecolor") || ARG("-forcecolour"))
+        {
+            vlog_toggle_color(1);
+        }
+        else if (ARG("-nocolor") || ARG("-nocolour"))
+        {
+            vlog_toggle_color(0);
+        }
 #undef ARG_INNER
 #undef ARG
         else