Icepool

* Renamed from `hdroller` to `icepool`.
* Primary repository is now https://github.com/HighDiceRoller/icepool.
* Only `tuple`s become `VectorDie`.
* Weights of 10^30 or above are not shown in tables by default.

* Add `max_depth` parameter to `sub()`. If set to `None` this seeks a fixed point.
* Add `'reduce'` option for `denominator_method` parameters.
* Cache results of `repeat_and_sum()`.

* Add `ndim` keyword argument to `d()`.
* Removed `hitting_time()` method; it seems too niche to commit to.
* Several arguments are now keyword-only.
* Fix to `reroll_until()` for vector dice.

* Add `VectorDie.all()` and `VectorDie.any()`.
* More fixes to `ndim` calculation.

* `EmptyDie` (a die with no outcomes) is now its own class.
* `mix()` along with its weights argument is folded into the `Die()` factory.
* Fixes to `ndim` calculation.
* `apply(), EvalPool.final_outcome()` can now return dice, `hdroller.Reroll`, etc.
* Center `Ellipsis` when indexing a pool can now work on undersized pools, rather than being an error.
* Fix `lcm_weighted` denominator method.
* `len(die)` is now the same as `die.num_outcomes()` again.
* Slicing a die now refers to (sorted) outcome indexes.
* Dimension slicing is now `VectorDie.dim[select]`.

* `Die()` now takes a variable number of arguments. A sequence provided as a single argument will be treated as a single outcome equal to that sequence.
To have one outcome per item in the sequence, the sequence must be unpacked into multiple arguments.
* `min_outcome` and `ndim` args to `Die()` are now keyword-only.
* Non-integers are now allowed for `count_dice`. Use at your own risk.
* The third argument to a `count_dice` slice, if provided, changes the size of the pool.
* Up to one `Ellipsis` (`...`) may now be used in `count_dice`. This allows the tuple option to adapt to differently-sized pools.
* `VectorDie` outcomes are now unpacked when providing them to callable arguments in `reroll()`, `explode()`, `split()`.
* `if_else()` is now a method of `ScalarDie` rather than a free function.
* Fixed the invert operator.