Release 3.2.4

• Separate RDF::Literal handling from Context#expand_value directly into FromRDF#resource_representation.
• Pass through RDF literals in ToRDF#item_to_rdf.
• Use internalRepresentation option in fromRdf to preserve raw RDF literals as values.
• Use context loader when loading contexts.
• Add allowed_content_types keyword argument to loadRemoteDocument to allow additional content types to be considered valid.
• Add Context#to_rb tests, and make sure preloaded context has a context_base.
• Update dependencies and relax dependencies on rack and sinatra.
• fix(performance): comment all log_debug (@abrisse)