Collapses 2.13 and 2.14 into one and changes the wording of the rule to ...

...be positive.


    Collapses 2.13 and 2.14 into one and changes the wording of the rule to be positive.
    Rewords 1.8 so that it is simpler and positively worded.
    Reformulates 1.9 in the same wording as 2.13.

Also includes minor reformatting.

As discussed in #106, with positive rule focus suggested by @DougLea

Review by @reactive-streams/contributors