Create _OrzCmdName global variable to keep the commands supported by this script.
[Feature] Completion framework support in bash shell
<Note>
  1. Automatically setup completion function according to _OrzCmdName[@] command list variable.
  2. The completion function name format is _Orz_<Command_Name>__comp().
  3. It will do nothing if _Orz_<Command_Name>__comp() not defined in this shell script.
[Feature] Completion framework support in bash shell

Add two common completion helper functions.
  1. _Orz__Comp_gen_reply()
  2. _Orz__Comp_has_doubledash()