fix(colors): treat no-color mode as no-color instead of narratable (#94)

Fixes: https://github.com/zkat/miette/issues/93

BREAKING CHANGE: NO_COLOR no longer triggers the narrated handler. Use
NO_GRAPHICS instead.

src/handler.rs

@@ -188,8 +188,8 @@ impl MietteHandlerOpts {
             !force_narrated
         } else if let Some(force_graphical) = self.force_graphical {
             force_graphical
-        } else if let Some(info) = supports_color::on(Stream::Stderr) {
-            info.has_basic
+        } else if let Ok(env) = std::env::var("NO_GRAPHICS") {
+            env == "0"
         } else {
             false
         }