Use tracing crate for logging (#1192)

* egui_web: use tracing crate
* egui_glow: use tracing crate
* Log at the debug level
* egui_demo_app: enable tracing to log to stdout
* Use tracing in egui-winit
* Add opt-in tracing support to egui

egui_glow/src/shader_version.rs

@@ -1,5 +1,5 @@
 #![allow(unsafe_code)]
-use crate::misc_util::glow_print;
+
 use glow::HasContext;
 use std::convert::TryInto;
 
@@ -17,10 +17,11 @@ impl ShaderVersion {
         let shading_lang_string =
             unsafe { gl.get_parameter_string(glow::SHADING_LANGUAGE_VERSION) };
         let shader_version = Self::parse(&shading_lang_string);
-        glow_print(format!(
+        tracing::debug!(
             "Shader version: {:?} ({:?}).",
-            shader_version, shading_lang_string
-        ));
+            shader_version,
+            shading_lang_string
+        );
         shader_version
     }