Review request for JDK-8139888: Improve Dynalink JavaDoc some more

[Attila Szegedi]

Please review JDK-8139888 "Improve Dynalink JavaDoc some more" at <http://cr.openjdk.java.net/~attila/8139888/webrev.jdk9> for <https://bugs.openjdk.java.net/browse/JDK-8139888>

This is the last anticipated JavaDoc focused changeset.

In addition to JavaDoc improvements, there are few minor changes:
- DynamicLinkerFactory rejects nulls in lists of linkers being passed 
- LinkRequest.replaceArguments was made variable arity (taking Object… as its last arg instead of Object[]), making it consistent with SipleLinkRequest constructor
- SimpleLinkRequest rejects nulls in constructor parameters now, and clones incoming arguments lists
- Lookup and NameCodec classes were made final
 
Thanks,
  Attila.