Add place holder for where age adjustment will happen
First attempt at final step in calculating projection

The results still need to be age adjusted and re-baselined to the league
average of the most recent year.
Allow specifying input and output files

Need to save the projections somewhere! There needs to be logic to check
the input file exists and the output file is specified.
Save the year used for indexing batters

Save the index year so there's a known index that can be used later.
Save an overall mapping of player => row index
Write the projection out