file_close() now returns an integer.
Clarified & refactored init_args() a bit.
Added `init.mind` to make the init file accessible to the program.
Moved command line handling to the files args.{ch}.
Documentation bug: `/filestream' -> `/textfile'
Added constructors for text stream objects.

- Text streams now contain a reference to the file from which they were
  constructed
- New kernel words are `file-init`, `>caller`, `body>`, `>body`.