PLT Web Server Documentation Reorganization

The PLT Web Server was one of the first systems to get documented in Scribble, which was very convenient compared to the old documentation. However, it was organized too much like a reference manual with little guide to a user to understand how some modules fits in to the big picture. I've reorganized the documentation with the following paradigm:

• Running the Web Server
• Writing Servlets
• Extending the Web Server

Other improvement related to this: I've added examples to almost every servlet function. I have integrated the stateless and non-stateless servlet documentation to put stateless servlets on a more secure footing and make it clear that they are usable in real applications. I've created an HTTP sub-module that encapsulates most of the HTTP handling. (This will limit the need to use what used to be considered internal Web Server functions.)