Hello,

This patch adds a `setq`-like equivalent to `pcase-let`.  This is
convenient when one wants the bindings to exist outside of a `let` form.

This macro expands into multiple `setq` calls that are combined where
possible.


     ;; => (1 2 3 4)
     (let (a b c d)
       (pcase-setq a 1
                   b 2
                   `[,c ,d] [3 4])
       (list a b c d))


Please let me know what should be changed.

Thank you.