Tasks removed as DONE from wiki

[Jose E. Marchesi]

FYI, I have removed the following tasks from
https://gcc.gnu.org/wiki/Algol68FrontEnd, because they have already
done:

 * Add support for reading .a archives to a68-imports.cc. The go front-end has code for this.
 * Error on overflow in integral denotations.
 * Adopt backslash as alt representation for `of' As suggested by Hansen in AB427.
 * SET and CLEAR dyadic operators for `SIZETY bits'.

Salud!