Use compactArrays as explicit input parameter in Compaction Algorithm

Previously, the algorithm didn't have a dedicated parameter but used language like "if array compaction has been requested" without specifying how that might be done. I could have used a variable but I choose to directly link to the corresponding option in JsonLdOptions instead.

@gkellogg, let me know if you think that couples the algorithms and the API too much.

This addresses #218.