Reinforcement learning (RL) isn't covered much in Julia packages. There is a collection of RL algorithms over MDP in package:
https://github.com/cpritcha/MDP. There is a collection of IJulia notebooks from a Stanford course that cover more RL algorithms:
https://github.com/sisl/aa228-notebook/tree/masterUnfortunately, more advanced function approximation techniques, beyond look-up table, that allow to tackle large action-state spaces, are nowhere to find.
Couple a month ago, Shane Conway, the guy behind RL-Glue, talked about developing Julia RL-Glue client. If that happens, it would be quite simple to use various advanced RL algorithms, including value function approximators, in Julia.