Maps join functions

[analyticbastard]

Functions to join map in a similar way to SQL

(let [a {:a 1 :b 2}
      b {1 "a" 3 "c"}]
  (m/inner-join a b))
=> {:a "a"}

Supports transitive relationshipts

[weavejester]

Thanks for the patch, but I think these functions are a little too specialised for Medley.