Changed the List objects to IEnumerables

Changing to IEnumerables reduces some superfluous method calls to create
the refinements/ranges. For example, keywords.Select(x =>
x.ID.ToString()) instead of keywords.Select(x =>
x.ID.ToString()).ToList()
Merge pull request #26 from andrewburgess/type-relaxing

Changed Refinements/Ranges to IEnumerables