logging: first outlet receives logger error message

Abandons stderr special-casing:

* looks weird on shell and IO redirection to same file because of
interleaving of stdout and stderr
* better than a separate dedicated outlet because it does not require
additional configuration

fixes #28

BREAK SEMANTICS CONFIG

docs/configuration/logging.rst

@@ -27,6 +27,10 @@ Check out :sampleconf:`random/logging.yml` for an example on how to configure mu
     
     jobs: ...
 
+.. ATTENTION::
+    The **first outlet is special**: if an error writing to any outlet occurs, the first outlet receives the error and can print it.
+    Thus, the first outlet must be the one that always works and does not block, e.g. ``stdout``, which is the default.
+
 Default Configuration
 ---------------------
 
@@ -41,10 +45,6 @@ By default, the following logging configuration is used
           level:  "warn"
           format: "human"
 
-.. ATTENTION::
-    Output to **stderr** should always be considered a **critical error**.
-    Only errors in the logging infrastructure itself, e.g. IO errors when writing to an outlet, are sent to stderr.
-
 Building Blocks
 ---------------