Moved CFile buffer header declaration to separate header file
Added more documentation on what cfile_buffer_alloc does, and what it needs
from a read function, and a parameter for the total size of the buffer (rather
than just the size of the last read).  This allows different implementations
to have different buffer sizes, as well as the buffer to be set somehow when
opening the file.
Added buffer allocation code.  Further routines to be added.