Delete some old code

The merge_* functions are also old code, but need to decide what to do
about updating with new years. I think if things are done in batches
consisting of whole years, then can just concatenate the new files with
the old.
Add another clarifying comment

The stats dict might be able to be reduced. Might leave it in a bit
longer to see if it's useful for other things or not.
Delete unused import and rearrange another

Deleted an unused import and rearranged another so the two almost
superfluous imports are together. Once the merge_* functions are gone,
those two imports will be deleted.
Yield the year as an integer
Separate stats for players by the season
Convert a number of game fields to integers
Crude dumping of stats

Missing a header and some stats, but don't know which, are zero for the
player's season. The stats tracked needs to be contained better. I went
away from that method in preference for dicts, but when saving things,
all of the stats need to be recorded.