Implement a file system, part 1.

For this step only a very basic file system is needed, but it will
become more sophisticated in the future, so don't over-simplify
or you'll have to change nearly everything. It should operate on
an emulated disc (like "an emulated disc drive" from class 3), so
mistakes won't do any harm.

The file system should be implemented as a library of functions
that could be used by programs instead of the standard low-level
input/output functions such as open, read, write, close, etc.

At this stage you only need to support plain text files in a
single root directory. Subdirectories will come later. 

Required functionality:

* Create a new emulated disc drive and format it
  don't forget to create an empty root directory and provide
  some way of knowing which blocks are free.

* Create a new file

* Add data to an existing file

* Read the contents of a file

* List the root directory

* Delete a file

Develop incrementally. Gradually build on little successes and it
is relatively easy.

Along with your code and test program(s) also submit some small 
documentation describing your disc and file structures, and the
important functions, and including your still-to-be-done list.