Make the Person constructor explicit

Why make things more complicated than they have to be?
Handle tied games

Modifies get_winner and get_loser to return boost optional, which can be
empty if the game is tied.

This might support 'in-progress' games down the road.

Fixes #2.
Remove extra debug includes
Build as a shared library by default
Rename person to player

The only people we've interacted with so far have been players, so the
split is getting confusing.
Add travis build configuration

Due to travis-ci/travis-ci#979, we can't build yet since we depend on
c++11. Will wait on that issue before starting CI.