Replaced "filestream" with "textfile".
Documentation of previously defined words. Introduction of `link>`.

The documented words are `>link`, `link>`, `>name`, `>doer`, `>body`,
`body>`, `file-init` and `>caller`

Fixed wrong definitions of `>name`, `>body` and `.name`.
Removed comments that were notes for a future that will not be.
Fixed typo.
Some rearrangements and refactoring.
If `file-forward` reaches EOF, the file is now closed automatically.
Separated booting and abort.

`boot` is now a Defer. It is executed when "init.mind" has been read.