This function returns a character vector of the usernames of the game winners
get_winner(result_column, white, black)
A character vector in the extracted data frame called 'Result'
A character vector in the extracted data frame called 'White' for the player on white
A character vector in the extracted data frame called 'Black' for the player on black
A character vector of the game ending for each game
if (FALSE) {
get_winner(df$Result, df$White, df$Black)
}