Collapse collapse ranges overlapping or adjacent.

Full returns a full span crossing the key space.

NewFullWith creates a set of a subset of spans.

Overlaps checks whether two spans have overlapped part.

Sorted takes the ownership of a raw `ValuedFull` and then wrap it with `ValueSorted`.

Valued is span binding to a value, which is the entry type of span tree.

ValuedFull represents a set of valued ranges, which doesn't overlap and union of them all is the full key space.

ValueSortedFull is almost the same as `Valued`, however it added an extra index hence enabled query range by theirs value.

Span is the type of an adjacent sub key space.

Value is the value type of stored in the span tree.