Update pt.terrier.Retriever __str__ and __repr__

[cmacdonald]

{wip}

These will be viewable by all users who dont use names=[] in -pt.Experiment()

[cmacdonald]

Here is what a new new experiment looks like:

>>> pt.Experiment([br, br >> pt.rewrite.Bo1QueryExpansion(br.indexref) >> br], dataset.get_topics(), dataset.get_qrels(), ["map"])
                                                name       map
0                                     pt.t.Retr(DPH)  0.283614
1  Compose(Compose(pt.t.Retr(DPH), QueryExpansion...  0.295955

[seanmacavaney]

Let me think a bit on this...

On the one hand, it's nice to have short, abbreviated names here to be concise.

On the other hand, the current form might look too much like an actual python statement -- and pt.t.Retr doesn't exist.

How about TerrierRetr(DPH)? Only 2 characters longer.

[cmacdonald]

How about TerrierRetr(DPH)? Only 2 characters longer.

The featured one is much longer of course.

[seanmacavaney]

TerrierFeatRetr?