Update README.md

Updating README.md to point to the 0.4.0 release for the interfaces
Fixes #114 by removing the outdated test in the TCK and adding guideline for cancellation propagation for Processor to the README.
Adds RELEASE-NOTES.md which is intended to contain release information from 1.0.0 and forwards.
Rule 3.12 verification in subscriber whitebox now really checks it
This verification is now moved to PublisherVerification, as it's a
publishers behavior (*it* must stop emiting, not the subscriber).

Resolves #115
Fail test in case of double onError/onComplete signals
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.
Merge pull request #120 from reactive-streams/wip-fix-111-√

Adds RELEASE-NOTES.md which is intended to contain release information f...
Merge pull request #117 from reactive-streams/wip-106-√

Collapses 2.13 and 2.14 into one and changes the wording of the rule to ...
Merge pull request #119 from reactive-streams/wip-fix-114-√

Fixes #114 by removing the outdated test in the TCK and adding guideline...
Merge pull request #121 from ktoso/wip-rule312-for-reals-ktoso

Rule 3.12 verification in subscriber whitebox now really checks it
Merge pull request #122 from ktoso/impr-fail-tck-when-onError-twice-ktoso

Fail test in case of double onError/onComplete signals
Add in-spec hyperlinks to make it more navigable
Merge pull request #123 from ktoso/spec-more-links-ktoso

Add in-spec hyperlinks to make it more navigable
fix #96
Merge pull request #97 from ouertani/enhance-javaDoc

Enhance java doc
=tck #128 TCK updated to reflect merged rules 2.13 and 2.14
=tck method names and fine-details in some specs improved
Updates CONTRIBUTING.md with Gatekeeper SLAs
Merge pull request #132 from reactive-streams/wip-129-update-contributing-√

Updates CONTRIBUTING.md with Gatekeeper SLAs
Merge pull request #131 from ktoso/wip-TCK-cleanups-ktoso

=tck method names and fine-details in some specs improved