Added coverage and metrics

* Added SimpleCov; C0 coverage is 99.72 (1 LOC in an else branch
  skipped)

* Added coverage metrics output folder for posterity

* Added metric_fu - flay found duplicate code in the CsvReader classes
  (known issue, but there it is); flog found a lot of complexity in
  BattingData

* Ran code through CodeClimate; all classes get an 'A' rating except
  for BattingData which gets a 'D' for complex methods and overall
  complexity. Some of this may be removable but some may not. Will
  investigate

* Ran metric_fu, which tracks flog/flay/reek/roodi/etc output over
  time. Plenty of code smells identified to be investigated

* Added tmp/ directory for posterity as well (also so the metric_fu
  data over time will make pretty graphs)