Upgrade maven-javadoc-plugin; fix a few javadoc warnings

[daveyarwood]

As I was releasing 0.5.2, I noticed some javadoc warnings:

[INFO] Note: Custom tags that could override future standard tags:  @apiNote. To avoid potential overrides, use at least one period character (.) in custom tag names.
[INFO] 7 warnings
[INFO] [WARNING] Javadoc Warnings
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/org/zeromq/ZMQ.java:833: warning - Tag @link: can't find Socket(Context, SocketType) in org.zeromq.ZMQ.Socket
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/org/zeromq/ZMQ.java:2213: warning - @param argument "chooser," is not a parameter name.
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/org/zeromq/ZStar.java:169: warning - Tag @link: can't find create(ZContext, Socket, int, Star, Object...) in org.zeromq.ZStar.Fortune
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/org/zeromq/proto/ZPicture.java:183: warning - Tag @link: can't find sendBinaryPicture(Socket, String, Object...) in org.zeromq.proto.ZPicture
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/org/zeromq/proto/ZPicture.java:280: warning - Tag @link: can't find recvPicture(Socket, String) in org.zeromq.proto.ZPicture
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/org/zeromq/proto/ZPicture.java:370: warning - Tag @link: can't find sendPicture(Socket, String, Object...) in org.zeromq.proto.ZPicture
[INFO] [WARNING] /home/dave/code/jeromq/target/checkout/src/main/java/zmq/io/net/tcp/TcpAddress.java:92: warning - @return tag has no arguments.

This fixes a few of those.

I wasn't able to make sense of the @link warnings. I tried a bunch of different syntaxes, and nothing seems to get rid of the warning. I barely understand what I'm doing, so maybe someone else will have more luck. :)

[coveralls]

Coverage decreased (-0.2%) to 85.169% when pulling 8a79f57 on daveyarwood:javadoc-fixes into 0e53911 on zeromq:master.

[coveralls]

Coverage decreased (-0.06%) to 85.294% when pulling 8a79f57 on daveyarwood:javadoc-fixes into 0e53911 on zeromq:master.