Fixed memory leak in LocationMap::remove

[ImmemorConsultrixContrarie]

Fixes #245.

The initial solution has obvious worst case: inserting a single entity and then removing it, which would allocate the block in the heap and then deallocate the same block.

What could be done about it:

1. Do nothing. Could be a good option, actually, because inserting a single entity is awfully ineffective and creates a unique block for any single insert anyway.
2. Use [T; N] instead of Box<[T; N]>. This would make hashmap storage slower to reallocate, but totally avoids single entity allocation problem and lessens indirection.
3. Make single entity a special case:

enum OneTooMany<T> { One(T), Many(Box<[T; N]>) }

[TomGillen]

If we keep a count next to each array, we could maintain that and remove the entry when the count becomes 0, rather than have to scan through the array to check for all nones on every remove.

[ImmemorConsultrixContrarie]

If we keep a count next to each array, we could maintain that and remove the entry when the count becomes 0, rather than have to scan through the array to check for all nones on every remove.

That's true and I had a thought about it, but that required too much code to write at the time.