JAVA-1391: Javadoc for driver-core

Started creating Javadoc for the core module.  Started with a simple search for invalid HTML to fix, and then moved on to documenting (most) of the connection package.
"that match the criteria of the implementing ServerSelector" is an awkward phrasing.  It's enough to say:

"Select a list of server descriptions from the given cluster description according to some criterial.