Improve docstrings of MAKE-RANDOM-STATE and SEED-RANDOM-STATE.

Improve docstrings of MAKE-RANDOM-STATE and SEED-RANDOM-STATE.

The formatting of some item lists in the docstring of SEED-RANDOM-STATE
was broken in the manual. Fix the indentation of the docstring so that
the conversion to texinfo can correctly collect multiple lines belonging
to the same bullet points, and drop a "- " intended to indicate a
single-item list as that doesn't work (according to comments in
docstrings.lisp item lists must consist of at least two items).

Fix some small grammatical errors.

While MAKE-RANDOM-STATE's docstring is not in the manual, it consists
mostly of a part of SEED-RANDOM-STATE's docstring, so apply the fixes
there, too.