Don't fetch all of the hdf5 groups at once

This should improve memory use, but might have a negative impact on
performance. Likely a negligible effect.
Factor out a summarizing game's events into a function
Factor out error's fielding index

This gets the line length under 80 characters
Factor out involved player

Again makes one line shorter than 80 characters and gets another line
just over 80.
Oops, forgot to include these two variables in the refactor