Adds gitignore file
Fixes dup and checkmate? methods
Setup Chess and HumanPlayer classes
Adds row and column indicators on Board#render
Updates board#render with colorize
Split classes into new files
Adds error for moving opponent's piece
Refactoring and cleanup
Refactors Pawn. Better rendering
Defines custom errors
Fixes error bug
Removes piece_catalog. Fixes knight moves.