bug#31311: 27.0; doc of `pcase'

[Eli Zaretskii]

> From: Thien-Thi Nguyen <ttn@gnu.org>
> Date: Mon, 30 Apr 2018 15:35:32 +0200
> Cc: 31311@debbugs.gnu.org
> 
> Anyway, to start transforming discussion energy (pleasant or
> otherwise) into repo commits, i've just pushed branch
> ‘fix/bug-31311-pcase-doc’, w/ these commits:
> 
>  4ad382d 2018-04-30 add blank line before each @item in @table
>  8fccdaa 2018-04-30 rewrite @item @var{atom}
>  afb5aa4 2018-04-30 move UPattern and QPattern tables outside of @defmac pcase
>  0fa3538 2018-04-30 add blank line before each @item in @table

Thanks!