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

Cargo.lock

@@ -798,6 +798,7 @@ dependencies = [
  "nohash-hasher",
  "ron",
  "serde",
+ "tracing",
 ]
 
 [[package]]
@@ -809,6 +810,7 @@ dependencies = [
  "epi",
  "instant",
  "serde",
+ "tracing",
  "tts",
  "webbrowser",
  "winit",
@@ -820,6 +822,7 @@ version = "0.16.0"
 dependencies = [
  "eframe",
  "egui_demo_lib",
+ "tracing-subscriber",
 ]
 
 [[package]]
@@ -864,6 +867,7 @@ dependencies = [
  "glutin",
  "image",
  "memoffset",
+ "tracing",
  "wasm-bindgen",
  "web-sys",
 ]
@@ -880,6 +884,8 @@ dependencies = [
  "js-sys",
  "ron",
  "serde",
+ "tracing",
+ "tracing-wasm",
  "tts",
  "wasm-bindgen",
  "wasm-bindgen-futures",
@@ -972,6 +978,7 @@ dependencies = [
  "egui",
  "ron",
  "serde",
+ "tracing",
 ]
 
 [[package]]
@@ -1845,6 +1852,12 @@ version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d4fd5641d01c8f18a23da7b6fe29298ff4b55afcccdf78973b24cf3175fee32e"
 
+[[package]]
+name = "pin-project-lite"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e280fbe77cc62c91527259e9442153f4688736748d24660126286329742b4c6c"
+
 [[package]]
 name = "pkg-config"
 version = "0.3.24"
@@ -2199,6 +2212,15 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "sharded-slab"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "900fba806f70c630b0a382d0d825e17a0f19fcd059a2ade1ff237bcddf446b31"
+dependencies = [
+ "lazy_static",
+]
+
 [[package]]
 name = "shared_library"
 version = "0.1.9"
@@ -2416,6 +2438,15 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thread_local"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5516c27b78311c50bf42c071425c560ac799b11c30b31f87e3081965fe5e0180"
+dependencies = [
+ "once_cell",
+]
+
 [[package]]
 name = "time"
 version = "0.1.43"
@@ -2470,6 +2501,74 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "tracing"
+version = "0.1.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "375a639232caf30edfc78e8d89b2d4c375515393e7af7e16f01cd96917fb2105"
+dependencies = [
+ "cfg-if 1.0.0",
+ "pin-project-lite",
+ "tracing-attributes",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-attributes"
+version = "0.1.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f4f480b8f81512e825f337ad51e94c1eb5d3bbdf2b363dcd01e2b19a9ffe3f8e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "tracing-core"
+version = "0.1.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1f4ed65637b8390770814083d20756f87bfa2c21bf2f110babdc5438351746e4"
+dependencies = [
+ "lazy_static",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a6923477a48e41c1951f1999ef8bb5a3023eb723ceadafe78ffb65dc366761e3"
+dependencies = [
+ "lazy_static",
+ "log",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-subscriber"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5312f325fe3588e277415f5a6cca1f4ccad0f248c4cd5a4bd33032d7286abc22"
+dependencies = [
+ "ansi_term",
+ "sharded-slab",
+ "smallvec",
+ "thread_local",
+ "tracing-core",
+ "tracing-log",
+]
+
+[[package]]
+name = "tracing-wasm"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4575c663a174420fa2d78f4108ff68f65bf2fbb7dd89f33749b6e826b3626e07"
+dependencies = [
+ "tracing",
+ "tracing-subscriber",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "ttf-parser"
 version = "0.14.0"