Functionality for managing caching for compiled roll functions.

In many cases, ExDiceRoller can be used to compile a dice roll during project compilation, and using it within its local area, or pass it as an argument elsewhere. However, dice rolls can be generated during runtime. Repeated tokenizing, parsing, and compiling of runtime dice rolls can add up. The more complex the dice roll, the higher the cost.

Local testing has revealed that there can be a relatively signifcant performance savings by caching compiled dice rolls and reusing the cached values instead of repeated interpretation. While these savings are on the order of microseconds (not milliseconds), they can add up in applications that have complex rules and are regularly generating dice rolls during runtime.

In an effort to avoid this, ExDiceRoller allows for dice rolls to be cached and reused.

iex> ExDiceRoller.start_cache()
iex> ExDiceRoller.Cache.all()
[]
iex> ExDiceRoller.roll("2d6+1d5", cache: true)
9
iex> [{"2d6+1d5", _}] = ExDiceRoller.Cache.all()
iex> ExDiceRoller.roll("2d6+1d5", cache: true)
11
iex> [{"2d6+1d5", _}] = ExDiceRoller.Cache.all()
iex> ExDiceRoller.roll("1d4+x", [x: 3, cache: true])
7
iex> [{"1d4+x", _}, {"2d6+1d5", _}] = ExDiceRoller.Cache.all()
iex> ExDiceRoller.roll("1d4+x", [x: 3, cache: true])
7