Add get_{winning|losing}_score

This is needed in RRI calculations.
Update game to use unsigned int for scores
Change SpTeamPair to SpTwoTeams (array)

Can't iterate over a pair, and pairs are intended for mixed types,
generally.
Add weeks_after

This utility calculates the number of weeks later one date is than
another. This calculation isn't a pure date subtraction, since we first
rewind the earlier date to the start of the week (Monday), *then*
calculate the weeks afterwards.

We don't do fancy math, we actually iterate over the weeks and count, so
this might not (probably isn't) the best implementation. However, it's
hopefully correct, withtout worrying about Weird Date Stuff.
Use gregorian, not gregorian_types

In the event of an error, the date is used for IO, which fails w/o the
full include.
Add DatedGame typedefs to include/flatball/Common
Add team accessor to Game
Add documentation

This includes configuration for `make docs` as well as inline
documentation for classes.
RatePlayersBasic needs to inherit from RatePlayers

Before, the base class wasn't doing anything.
Fix typo: FLATBAL_ to FLATBALL_
Add base algorithm template class

This base class has both an inplace and copy versions, which can be used
as superclasses of algorithms.
Add TODO
Fix bad placement of documentation
Remove Player.cpp

Don't need it.
Remove TODO
Document our common typedefs
Use STRIP_FROM_INC_PATH to prefix header files

This is in the documentation, now any listing of header files will look
like `#include <flatball/Common.hpp>` instead of just `#include
<Common.hpp>`.
Use floats for ratings

Double just excessive, at least at this point.
Add RRI

The RRI is the USAU's team rating algorithm. Details are provided at
http://play.usaultimate.org/teams/events/rankings/#algorithm.

The implementation leaves a few details unspecified, including:

- What to do in the case of tied games
- How, exactly, to ignore blowout games of lower-rated teams. For
  instance, if a team has six games and they are all blowouts, do we
  ignore one of them? If so, which one?

However, this is a first pass at solutions, with much work still to be
done.

Closes #4