Convert Batter to Ruby 2.1 KWARGS

* Batter.find_all_by_* methods are now all private; use
  Batter.find_all() with keywords instead, e.g. Batter.find_all(team:
  "SEA", year: 2008)

* Hardened Batter API my making all nonessential / non-directly-tested
  class methods private (they are already tested indirectly, which is
  how private methods should be tested, if and when they exist)
Remove unexercisable error-handling path

* Batter used to access the CSV file and raise a helpful error message
  if an error condition (that never happens) happens; this has been
  removed

* This makes my teeth itch, however, because if the data files are
  changed out in future, the code would fail silently

* Pushed the problem down into Ruby's internals by changing
  Batter.find from calling batter_data[id] to calling
  batter_data.fetch(id), which will raise an error under the exact
  same conditions as batter_data[id] returning nil

* This caused the test suite to break, however, as there are 3 tests
  in BattingDataSpec that rely on being able to create a BattingData
  with no Batter--but BattingData surreptitiously knows about
  Batter.find and calls it! Naughty, naughty BattingData! But it's not
  easily exorcisable, so for now I've written the typical (crappy)
  test smell of stubbing out Batter.find in BattingDataSpec

* All of this gets us to 100% C0 coverage, yippee

* More importantly, however, it reduces a 5-line block of code to a
  single line in Batter.load_batting_data
Remove duplicate CSV Reader

* BattingCsvReader and BatterCsvReader both are identical and know
  nothing about the CSV data coming in, they accept a filename and
  return rows of data

* The files were character-for-character identical except for the
  class name

* In theory this is where the column-name conversion should be
  happening; I may bring the files back in future if/when I extract
  the file conversion knowledge from Batter

* Updated metric_fu output; however, it appears that flog and saikuro
  are not yet Ruby 2.1 compatible so metric_fu may be broken. I'll
  still keep it around, however, so that I can run the other tools
  manually (cane, roodi, etc)
Reduce StatsGrinder#triple_crown_winner complexity
Style cleanup in BattingData
Style cleanup in BatBoy
Refactor Batter

* Change played_any_games_*? methods to played_any_games?(keywords)

* Style cleanup in Batter