UMLR — Inconsistent document structure descriptions in section 6.4

There are a number of descriptions in section 6.4 on how to read the specification that are confusing or erroneous. In section 6.4.1 the structure of the generic Classifier Descriptions is said to contain a "Derivation" heading. There are no such headings, but it would be relevant to actually introduce them and move the derivations from the "Operations" part (where they are located now). It would also be clarifying to specify that the "Association Ends" part only lists the association ends owned by the class (and therefore navigable). And, as far as can be seen, all the other association ends in all Abstract Syntax diagrams are non-navigable from the class under discussion. In section 6.4.2 the last three rules could be simplified or removed. All association ends have an explicit multiplicity, so rule 6 can be deleted. There are also no unlabeled association ends, so the same applies to rule 7. There are no associations that are explicitly named, so the last rule should be rewritten (delete "that are not explicitly named,"). In the Abstract Syntax diagrams, the only association ends that are navigable are those owned by a Class. All ends owned by the Association itself are non-navigable. The arrow notation is redundant since it always occur together with a dot. It could also be interesting to remove the public visibility symbols that occur in all diagrams since they don't add any information if a "rule" was added instead. The diagrams would be slightly cleaner without the arrows and plus signs without losing any precision. Note that most of the diagrams in section 16 misses the dot notation (reported as a separate issue).