File handling functions are needed

[timbarnes]

Add file handling functions using the Forth Standard as a guide. Move as much to Forth as possible.

Basic functions required are:

• open-file
• close-file
• create-file
• read-line
• write-line
• read-file
• write-file
• r/o
• r/w
• s" should also work with files other than Forth

[timbarnes]

r/w and r/o are already implemented, but should be in Forth, simply placing a value on the stack.

The file-handle pointer should be moved to Forth, or eliminated in favor of user variables.

[timbarnes]

open-file, close-file, read-line and write-line have been implemented, as are file modes of r/w, r/o and w/o.
create-file remains to be implemented, and additional testing is required for all aspects of the system.