Consider making cprop cursors associative

[p-himik]

With plain maps, you can use any of the below options to get a value at a specific key:

(m :k)
(:k m)
(get m :k)

With cprop cursors, you can only use the first variant.

The change should be relatively straightforward - cursors can become structures that implement ILookup (no other interfaces are necessary unless you want to bridge the gap between cursors and maps even further) as well as IFn. Unless somebody uses fn? on cursors, this should be a non-breaking change.