title: implement similar thing like "help" command in python interactive shell
body: <p>I am implementing a shell which does similarly like python interactive shell. </p>
  
  <p>I am using raw_input and cmd2 library for it, now I need to implement a function which does exactly like "help" command. That is, it can show a large chunk of text which may exceed screen height and allow user to scroll down/up, and support Linux shell short-cut as well.</p>
  
  <p>I don't know if I can do it without involving curse library. If I have to, any suggestions to integrate it with raw_input, cmd2 library?</p>
  
  <p>thanks</p>