gap_data: Generate a gapdata class object from a dendrogram object
Description
This function takes a dendrogram class object as an input, and generate a gapdata class object as an output.
By parsing the dendrogram object based on parameters for gaps, gaps between leaves in a dendrogram are introduced,
and the coordinates of the leaves are adjusted. The gaps can be based on the a height (or distance) threshold to
to introduce the gaps of the same width, or quantitative mapping of distance values mapped linearly or exponentially.