#244 - Implicit navigator for maps

[jeff303]

Adding implicit navigator for PersistentArrayMap that builds up a navigator recursively, of the form:

(if-path (i/combine-two-navs (keypath key) (pred= value))

) Adding tests

[nathanmarz]

Don't think this kind of filtering is useful enough to make a new implicit nav for it. Not sure what use case implicit navs for maps should target – maybe for expressing multi-path more concisely though I'm not convinced of that.