The FS_Writer class takes a file name in its constructor, and
provides a C++ stream for writing the specified file. The difference between
using FS_Writer and an ofstream directly is that FS_Writer
supports an extensible architecture for writing files to locations other than
on disk. Unlike with FS_Reader, there are no default FS_Writer
implementations other than for accessing disk files. However it is possible
to write your own extensions.
Most of the functions of this class are for internal use only. Only
the functions listed below should be used in your code.