Estimate buffer width for each cover intervals.

[ognis1205]

Is your feature request related to a problem? Please describe.

This is not related to any problems. For now, buffer width for VP tree search is estimated for
entire data. But in practical datasets, preferable buffer width is computed for each intervals of
cover. VP tree construction is designed to handle data skew, this implies that the buffer width
would be change for different intervals.

Describe the solution you'd like

In ReebDiagram estimator, buffer width estimation will be done for each intervals.

Additional context

N/A