Rename algorithm files

Simple renaming to make things a bit clearer, (e.g. rate_teams -> rri).

Fixes #19
Add WITH_ALGORITHMS option

Its nice to make things customizable.

Fixes #20
Add a Season class

This class, for now, encapsulates a vector of games and a vector of
teams. We can't just store a vector of games, because there may be teams
that are not included in any games.

Future work includes (possibly) verifying that both teams in a game are
included in the team list (or automatically adding them?) and helper
functions for finding teams in the list. However, these design changes
need to be informed by use-cases.
Add UsauTeam with name and ID

Also add a WITH_USAU option for building USAU-specific extensions.