Log Message:
Changes 0.31:
* doc update

Changes 0.3:
* new cascading attribute for subcommands

Changes 0.2:
* New Feature: Cascading Subcommand
* Deprecated Feature: Long Option Subcommand (still work)
* Abundant DOCs

Changes 0.103:
* Release

Changes 0.102:
* Re-upload

Changes 0.10:
* Update document

Changes 0.09:
* Fix the command pattern used in help.