Javadoc JsonLdProcessor
Fix Sesame to call flatten instead of frame if flatten is specified

TODO: Support framing http://json-ld.org/spec/latest/json-ld-framing/
Add accessor and mutator for document loader, as it is an official part
of the interface
javadoc and internal documentation for JsonLdOptions
remove clone method that is not well supported in general refs #101
javadoc more of JsonLdApi
renaming for consistency with the rest of the core package
javadoc JSONUtils
rename URL to JsonLdUrl to avoid confusion with java.net.URL
rename to JsonUtils for consistency
rename test to match
Update README.md
manage the httpcore version to match httpclient dependencies
fix java-8 javadoc warnings and errors for core module
fix more javadoc warnings