Adding extractors to process player and batting stats file

Creating player extractor and add spec for it
Creating batting extractor to process batting file
adding initializer to map csv header to database field
Adding models, spec and fixture for batting stats
Adding service module to extractor and create object from csv file

Also adding rake task process input file from terminal
adding domain models and related spec
adding simplecov gem for test coverage and set development log to error
Adding model for batting stats and related spec

Adding relations and scopes for neccessary filter
Adding service layer for batting stats to calculate batting average and slug_percentage

This change include spec and some refactoring around ingest
Refactoring extractor to get calculation from new service layer
fixing spec and adding factory for batting stats
Adding bunch of rake tasks to get all results and moving any calculation to lib module
adding Installation and usage instruction