Adds Chrono package
Adds a "Result" type to lib.rs
creates helpful type aliases for Score, Boost, and Gravity.
Creates a "TimedScore" which is a value and time data for calculating
score over time. There are two forms of this, Boosted and Decaying.
Since a Score can either be decaying over time or have been boosted
recently and be kept from decaying for some time.
Also implements a BoostedScore and a DecayingScore, which are both
TimedScores which represent the different states. These are important
because you can't boost a BoostedScore for instance.
