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

...be positive.

Also includes minor reformatting.

Also reformulates 1.9 in the same wording as 2.13

As discussed in #106, with positive rule focus suggested by @DougLea

Review by @reactive-streams/contributors 
Remove the `spec214_failingOnErrorInvocation` methods from the TCK as well as part of this PR then?