More updates regarding configuration

doc/confarg.doxygen

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+/*! \page confarg Configuration - runtime arguments
+
+<P>The ALSA library can accept runtime arguments for some configuration
+blocks. This extension is on top of the basic syntax of the configuration
+files.<P>
+
+\section confarg_define Defining arguments
+
+Arguments are specified by id (key) @args and array values containing
+the string names of arguments:
+
+\code
+@args [ CARD ]	# or
+@args.0 CARD
+\endcode
+
+\section confarg_type Defining argument type and default value
+
+Arguments type is specified by id (key) @args and argument name. The type
+and default value is specified in the compound:
+
+\code
+@args.CARD {
+  type string
+  default "abcd"
+}
+\endcode
+
+\section confarg_refer Refering argument
+
+Arguments are refered by dollar-sign ($) and name of argument:
+
+\code
+  card $CARD
+\endcode
+
+\section confarg_example Example
+
+\code
+pcm.demo {
+	@args [ CARD DEVICE ]
+	@args.CARD {
+		type string
+		default "supersonic"
+	}
+	@args.DEVICE {
+		type integer
+		default 0
+	}
+	type hw
+	card $CARD
+	device $DEVICE
+}
+\endcode
+
+*/