make the download files compatible to mp3 players playing files in name sorted order

Fixed issues:

• prepend to mp3 file names zeros to achieve compatibility with mp3 players played files in name sorted order.

Install instructions:

To install download the asbook-0.0.3.xpi.zip file decompress it and then open xpi file with Firefox. Click on "Install" completed the installation.
Please note: Firefox since version 43 deny to install unsigned plugins
so you need change this behavior.

1. Type in Address bar about:config.
2. promise to be careful with settings with a click on the promise button
3. type in the search field of about:config "xpinstall.signatures.required" (without parentheses)
4. change the value of the settings from "true" to "false" with double click on the field
5. done. now you can install the plugin.