Replace scaled clique identifier count with stepped clique identifier count

[gaurav]

Closes #205.

• We slightly prefer phrase fields (pf) over query fields (qf), but this might be having a limited benefit for short texts like ours: "Once the list of matching documents has been identified using the fq and qf parameters, the pf parameter can be used to "boost" the score of documents in cases where all of the terms in the q parameter appear in close proximity." We should try to remove the pf entirely and see what happens.

May improve #161.