Changes required for Shen 21.0

[Bruno Deferrari]

List of changes:

• add (import-kl "dict") after the "sys" load in boot.lsp. Should there be an if so that it only happens for versions >= 21?
• rename exit to something else? (it is not part of the kernel anymore)
• rename read-char-code to shen.read-char-code.

I think thats all is needed, haven't found anything else so far.

[Robert Koeninger]

These were handled in #11.