[JAVA-1391/2/3] Fixed Javadoc so it builds under Java 8.
Reducing the memory needed by the build in the hope that travis will stop killing our jobs.
Created a check in the build to let us turn off running @Slow tests.  Using this setting for Travis so that we don't use too much memory / time for the build that we run there. Applied the @Slow annotation to any tests in core or driver that take longer than 0.5 seconds locally, or that use an unusually high amount of memory.
[JAVA-1391] Javadoc for com.mongodb.codecs package (added missing Javadoc). Also some tiny tidy ups, like making methods private and removing @SuppressWarnings where possible.
[JAVA-1410] Documenting com.mongodb.gridfs
JAVA-1405: Made RawBsonDocument a subclass of BsonDocument
JAVA-1405: Made BsonDocument equals, hashCode, and toString work properly with BsonDocumentWrapper and RawBsonDocument subclasses
JAVA-1405: Update BsonValue-related Codec and CodecProvider implementation to work properly with BsonDocument subclasses (BsonDocumentWrapper and RawBsonDocument)
JAVA-1406: fix jsWithScope in JSONReader