Feature/revise spec

DO NOT MERGE. FOR DISCUSSION ONLY. @zdne @honzajavorek Please comment.

This PR updates the SPEC based on @zdne and my multiple discussions and refinements.

It also pulls in the current README with some typo fixes. 

@zdne I basically forked and update your branch for this PR into master. Would you prefer I just fork off of master and just create a branch the only adds the spec? Let me know.
There is still a problem here. Given *Value* is *Variable Value* then it MUST NOT be followed by another type definition. For example, this would be invalid:

```
- property: *variable value (string)* (number) 
```

Or am I missing something?