Use the base option instead of the mistakenly used compactArrays option

... when setting the base.
Do not process expandContext twice

It is already processed in the algorithms of JsonLdProcessor's methods
Interpret objects that do not have a @context entry as the JSON-LD context when passed into the API functions

Previously, all context parameters required a valid context document, i.e., an object with a @context member. Now the value of such a member can be passed in directly.

This addresses #245