Clean up BattingData

* Reduce overall complexity signficantly

* integer properties are initted as a loop in initialize as send
  "#{key}=", data[key].to_i

* integer properties are added in a loop as send(key) +
  other.send(key)

* This may be an ill-advised code change; I've made the code tighter
  but less easily accessible to the reader. Adding a stat will be much
  easier now but changing the way stats are dealt with will be much
  harder due to the tightened looping

* This reduces overall flog for this file from 154.7 to 72.1, probably
  good for a grade raise from D to A- or B+ in CodeClimate -- another
  good example of good tools pushing not entirely in a great
  direction, but oh well. This improves the score, but I wish I could
  think of a prettier way to tighten it up