Updated README.md for clarity for <=2.2.4

Author: lamweili

README.md

@@ -3,21 +3,25 @@ streamroller
 
 node.js file streams that roll over when they reach a maximum size, or a date/time.
 
-        npm install streamroller
+```sh
+npm install streamroller
+```
 
 ## usage
 
-        var rollers = require('streamroller');
-        var stream = new rollers.RollingFileStream('myfile', 1024, 3);
-        stream.write("stuff");
-        stream.end();
+```javascript
+var rollers = require('streamroller');
+var stream = new rollers.RollingFileStream('myfile', 1024, 3);
+stream.write("stuff");
+stream.end();
+```
 
 The streams behave the same as standard node.js streams, except that when certain conditions are met they will rename the current file to a backup and start writing to a new file.
 
 ### new RollingFileStream(filename [, maxSize, numBackups, options])
 * `filename` (String)
 * `maxSize` - the size in bytes to trigger a rollover, if not provided this defaults to MAX_SAFE_INTEGER and the stream will not roll.
-* `numBackups` - the number of old files to keep
+* `numBackups` - the number of old files to keep (excluding the hot file)
 * `options` - Object
   * `encoding` - defaults to 'utf8'
   * `mode` - defaults to 0644
@@ -48,10 +52,10 @@ When filename size >= maxSize then:
 	* `encoding` - defaults to 'utf8'
 	* `mode` defaults to 0644
 	* `flags` defaults to 'a' (see [fs.open](https://nodejs.org/dist/latest-v8.x/docs/api/fs.html#fs_fs_open_path_flags_mode_callback) for more details)
-    * `compress` - (boolean) compress the backup files, defaults to false
+    * `compress` - (boolean) defaults to `false` - compress the backup files using gzip (files will have `.gz` extension).
     * `keepFileExt` - (boolean) defaults to `false` - keep the file original extension. e.g.: `abc.log -> abc.2013-08-30.log`.
-	* `alwaysIncludePattern` - (boolean) extend the initial file with the pattern, defaults to false
-  * `daysToKeep` - (integer) if this is greater than 0, then files older than `daysToKeep` days will be deleted during file rolling.
+	* `alwaysIncludePattern` - (boolean) extend the initial file with the pattern, defaults to `false`
+  * `daysToKeep` - (integer) the number of old files that matches the pattern to keep (excluding the hot file)
 
 
 This returns a `WritableStream`. When the current time, formatted as `pattern`, changes then the current file will be renamed to `filename.formattedDate` where `formattedDate` is the result of processing the date through the pattern, and a new file will begin to be written. Streamroller uses [date-format](http://github.com/nomiddlename/date-format) to format dates, and the `pattern` should use the date-format format. e.g. with a `pattern` of `".yyyy-MM-dd"`, and assuming today is August 29, 2013 then writing to the stream today will just write to `filename`. At midnight (or more precisely, at the next file write after midnight), `filename` will be renamed to `filename.2013-08-29` and a new `filename` will be created. If `options.alwaysIncludePattern` is true, then the initial file will be `filename.2013-08-29` and no renaming will occur at midnight, but a new file will be written to with the name `filename.2013-08-30`.