Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
edited
| 7      | Once a terminal state has been signaled (`onError`, `onComplete`) it is REQUIRED that no further signals occur. Situational scenario MAY apply [see 1.21] |

added
| 21     | A failing `onComplete` (e.g. rising an exception) is a specification violation and MUST signal `onError` with `java.lang.IllegalStateException` |