Update javadocs

[ci skip]
pub/sub work.
Merge branch 'zeromq-master'

Conflicts:
	src/main/java/org/zeromq/api/Context.java
	src/main/java/org/zeromq/api/Receivable.java
	src/main/java/org/zeromq/api/Socket.java
updated code to latest from the origin repo.
cleaned up redundant variable.