elixir-lang/elixir — pull request #2748 by sean-lin (2014-09-03 06:49:59+00:00)
Title: Map backend config for Logger

I want to write a file backend for the Logger.
The backend config of Logger is a litte verbose. I must define a ID for backend and then use it to find out the specific config.

with this patch, I can do this
```
config Logger,
backends: [
%{mod: FileBackend, id: :error_log, file: "error.log", size: 1024},
%{mod: FileBackend, id: :debug_log, file: "debug.log", size: 10240},
]
```