Polish hello_world C program

Change the #include macro to be more suggestive of importing a system library.
Split two statements across two lines in the file.
Add hello world program.

This new hello_world program contains a pointer to an array of characters. It
also demonstrates a basic usage of const-correctness.
Add an extremely simple module

This module does little more than demonstrate how to create a loadable module.
Add a simple proc file.

This proc file can be created and destroyed by inserting and removing a module
from the kernel. The proc file does nothing useful (it prints out a series of
even numbers), but it can serve as an excellent template for studying how
virtual files work and for creating new proc files.