Add version from other project

This was mostly what I implemented as utility library for another
project. But I figured I can also extract it as it's useful on its
own.

examples/simple.rs

@@ -0,0 +1,22 @@
+
+mod config {
+    use std::path::PathBuf;
+
+    confique::config! {
+        log: {
+            /// Determines how many messages are logged. Log messages below
+            /// this level are not emitted. Possible values: "trace", "debug",
+            /// "info", "warn", "error" and "off".
+            level: log::LevelFilter = "debug",
+
+            /// If this is set, log messages are also written to this file.
+            #[example = "/var/log/tobira.log"]
+            file: Option<PathBuf>,
+        }
+    }
+}
+
+
+fn main() {
+
+}