add updated wording referencing SSIZE_MAX and _POSIX_SSIZE_MAX

add wording relating these two in discussion and in the P/R wording



I'm not entirely sure the wording is still correct as ammended. I added the link to the POSIX limits.h specification in the discussion where it mentions the minimum value for SSIZE_MAX as _POSIX_SSIZE_MAX but I'm unsure whether that information should be represented in the P/R. I am also unsure whether I should have moved the previous P/R into a blockquote above the resolution as a "Previous Resolution" and ammended the Resolution section instead.