doc: document Console class

document Console class to tell user can use it.

PR-URL: #1388
Fixes: #1359
Reviewed-By: Roman Reiss <me@silverwind.io>

Author: JacksonTian

doc/api/console.markdown

@@ -1,12 +1,22 @@
-# console
+# Console
 
     Stability: 2 - Stable
 
+The module defines a `Console` class and exports a `console` object.
+
+The `console` object is a special instance of `Console` whose output is
+sent to stdout or stderr.
+
+For ease of use, `console` is defined as a global object and can be used
+directly without `require`.
+
+## console
+
 * {Object}
 
 <!--type=global-->
 
-For printing to stdout and stderr.  Similar to the console object functions
+For printing to stdout and stderr. Similar to the console object functions
 provided by most web browsers, here the output is sent to stdout or stderr.
 
 The console functions are synchronous when the destination is a terminal or
@@ -22,7 +32,7 @@ In daily use, the blocking/non-blocking dichotomy is not something you
 should worry about unless you log huge amounts of data.
 
 
-## console.log([data][, ...])
+### console.log([data][, ...])
 
 Prints to stdout with newline. This function can take multiple arguments in a
 `printf()`-like way. Example:
@@ -34,19 +44,19 @@ Prints to stdout with newline. This function can take multiple arguments in a
 If formatting elements are not found in the first string then `util.inspect`
 is used on each argument.  See [util.format()][] for more information.
 
-## console.info([data][, ...])
+### console.info([data][, ...])
 
 Same as `console.log`.
 
-## console.error([data][, ...])
+### console.error([data][, ...])
 
 Same as `console.log` but prints to stderr.
 
-## console.warn([data][, ...])
+### console.warn([data][, ...])
 
 Same as `console.error`.
 
-## console.dir(obj[, options])
+### console.dir(obj[, options])
 
 Uses `util.inspect` on `obj` and prints resulting string to stdout. This function
 bypasses any custom `inspect()` function on `obj`. An optional *options* object
@@ -62,15 +72,15 @@ object. This is useful for inspecting large complicated objects. Defaults to
 - `colors` - if `true`, then the output will be styled with ANSI color codes.
 Defaults to `false`. Colors are customizable, see below.
 
-## console.time(label)
+### console.time(label)
 
 Used to calculate the duration of a specific operation. To start a timer, call
 the `console.time()` method, giving it a name as only parameter. To stop the
 timer, and to get the elapsed time in milliseconds, just call the
 [`console.timeEnd()`](#console_console_timeend_label) method, again passing the
 timer's name as the parameter.
 
-## console.timeEnd(label)
+### console.timeEnd(label)
 
 Stops a timer that was previously started by calling
 [`console.time()`](#console_console_time_label) and print the result to the
@@ -85,15 +95,48 @@ Example:
     console.timeEnd('100-elements');
     // prints 100-elements: 262ms
 
-## console.trace(message[, ...])
+### console.trace(message[, ...])
 
 Print to stderr `'Trace :'`, followed by the formatted message and stack trace
 to the current position.
 
-## console.assert(value[, message][, ...])
+### console.assert(value[, message][, ...])
 
 Similar to [assert.ok()][], but the error message is formatted as
 `util.format(message...)`.
 
+## Class: Console
+
+<!--type=class-->
+
+Use `require('console').Console` or `console.Console` to access this class.
+
+    var Console = require('console').Console;
+    var Console = console.Console;
+
+You can use `Console` class to custom simple logger like `console`, but with
+different output streams.
+
+### new Console(stdout[, stderr])
+
+Create a new `Console` by passing one or two writable stream instances.
+`stdout` is a writable stream to print log or info output. `stderr`
+is used for warning or error output. If `stderr` isn't passed, the warning
+and error output will be sent to the `stdout`.
+
+    var output = fs.createWriteStream('./stdout.log');
+    var errorOutput = fs.createWriteStream('./stderr.log');
+    // custom simple logger
+    var logger = new Console(output, errorOutput);
+    // use it like console
+    var count = 5;
+    logger.log('count: %d', count);
+    // in stdout.log: count 5
+
+The global `console` is a special `Console` whose output is sent to
+`process.stdout` and `process.stderr`:
+
+    new Console(process.stdout, process.stderr);
+
 [assert.ok()]: assert.html#assert_assert_value_message_assert_ok_value_message
 [util.format()]: util.html#util_util_format_format