emacs: Update pass website URL
emacs: Use when instead of if/progn
emacs: Use PASSWORD_STORE_CLIP_TIME env variable

Timeout password after PASSWORD_STORE_CLIP_TIME seconds, if set.
Otherwise timeout after 45 seconds. These are the setting used by pass.
Use APG instead of pwgen for password generation

APG offers a nice "pronounceable" password generation option, and I'd like to
use it with password-store.
tests: fix t0010 with APG
tests: fix t0500 with APG

APG can't generate passwords longer than 255 characters.