Correct enum value lookup for INT enums

[gbirchmeier]

also add unit tests for a variety of field types

should resolve #25

[CLAassistant]

All committers have signed the CLA.

[gbirchmeier]

JRuby env notes (mostly for myself):

To get a dev env, I used this compose and bash-shelled into it.

3015 ~/fork/fix_spec$ more docker-compose.yml 
name: fix-spec

services:

  app:
    image: jruby:9
    shm_size: 128mb
    ports:
      - 4567:4567
    volumes:
      - ./:/fix_spec
    tty: true

Probably jruby:10 would work, but I didn't want to upgrade more than necessary.

Then I had to do some updates to get bundler to stop being screwy.

gem update --system
gem install bundler
bundle update --bundler
bundle install

I think that is what did it.

[gbirchmeier]

I see @cbusbey 's name is still on our CLA, I'll try to get that long-overdue change in motion.