Deprecate Target::Pipe since it is broken

Author: jplatte

src/fmt/writer/mod.rs

@@ -20,6 +20,10 @@ pub enum Target {
     /// Logs will be sent to standard error.
     Stderr,
     /// Logs will be sent to a custom pipe.
+    #[deprecated = "\
+        This functionality is [broken](https://github.com/env-logger-rs/env_logger/issues/208) \
+        and nobody is working on fixing it\
+    "]
     Pipe(Box<dyn io::Write + Send + 'static>),
 }
 
@@ -37,6 +41,7 @@ impl fmt::Debug for Target {
             match self {
                 Self::Stdout => "stdout",
                 Self::Stderr => "stderr",
+                #[allow(deprecated)]
                 Self::Pipe(_) => "pipe",
             }
         )
@@ -60,6 +65,7 @@ impl From<Target> for WritableTarget {
         match target {
             Target::Stdout => Self::Stdout,
             Target::Stderr => Self::Stderr,
+            #[allow(deprecated)]
             Target::Pipe(pipe) => Self::Pipe(Box::new(Mutex::new(pipe))),
         }
     }