Adding array setters for terms

Previously setting a value by array index would fail silently. Now you
can set properties with []= (e.g. ```subject.title[1] = 'A title'```).
Accept terms passed into #set_value

Passing a term into Resource#set_value previously resulted in
unexpected behavior. This fixes that to set the current property to the
term's values, as though from an array.

Conflicts:
	spec/active_triples/resource_spec.rb
Refactoring tests for array setters
Merge pull request #46 from no-reply/feature/term_array_setters

Adding array setters for terms