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.
There are not parameters though.  I really do not want to go through and make these all final, since we have not configured checkstyle to do that.  I also don't see a big benefit, as I don't think I've ever accidentally modified an exception reference in a catch clause.