Update rx for #61

This is a cursory upgrade and could be taken further. The tests all
pass, but I want to make sure this really works before cleaning up
further.
Move pigpen.pig/eval-string to pigpen.runtime
Update code$ to not refer to pig classes. Using keywords instead
Use multimethods for serialization. Each platform implements these.
Merge pull request #72 from Netflix/change-code-dispatch

Update code$ to not refer to pig classes. Using keywords instead
Merge pull request #73 from Netflix/generalize-serialization

Use multimethods for serialization. Each platform implements these.
Move pigpen.pig/args->map and pigpen.pig/debug to pigpen.runtime
Merge pull request #74 from Netflix/move-util-fns

Move pigpen.pig/args->map and pigpen.pig/debug to pigpen.runtime
Move tuples & bags to post-processing & the UDF. Move exec to runtime.
Merge pull request #75 from Netflix/move-exec

Move tuples & bags to post-processing & the UDF. Move exec to runtime.
Merge branch 'upgrade-rx' of github.com:daveray/PigPen into daveray-upgrade-rx
Update more code to use rx bindings. Remove *max-load-records*!
Remove load-pig & store-pig
Require ns before protocol
Use array-map for tests
Clean up unsubscription
Merge branch 'upgrade-rx' into update-deps

* upgrade-rx:
  Clean up unsubscription
Update dependencies
Merge pull request #77 from Netflix/upgrade-rx

Upgrade rx
Merge pull request #78 from Netflix/update-deps

Update dependencies