Clusteval

* fix for dendrogram cut in special cases

* bug Fix in case no clusters are detected

Huge structural update.
The input parameter "method" can only be used for the evaluation of methods, such as silhouette, dbindex and derivative. The clustering approach can separately be chosen using the input parameter "cluster", which can be: agglomerative, kmeans, dbscan, hdbscan.

* added input parameter: "cluster"
* input parameter "method" is for: silhouette, dbindex, derivative
* Changed input parameter minclusters to min_clust
* Changed input parameter maxclusters to max_clust
* Pep8 styling
* code refactoring
* Docstrings updated

* dendrogram plotting possible
* Docstring updates

* Fix for hdbscan plotting

Huge and happy update in clusteval

* Code refactored into classes
* docstrings updated
* plot centralized
* scatter centralized
* code cleaning
* examples added

Have fun!