D3graph

* Fix for creating colors based on clustering
* Fix for import 'bigbang' example
* Internal name convention: `network_charge `to `charge `and `network_collision `to `collision`

* Renamed function _showfig to showfig
* By importing examples it will consistently output 2 parameters (adjmat and df)
*

* fix for ValueError from Jinja PackageLoader issue 14

* Added functionality to hide the slider in output HTML

More information can be found in the [documentation](https://erdogant.github.io/d3graph/pages/html/Examples.html#hide-slider).

* added scaler
* fixes for markers
* many fixes by rjhear
* name conventions (cluster_label into group)
* docstrings updated
* Added unit test

* New feature: Different edge markers (circle, arrow, square, stub) can now be set for marker_end.
* Name convention: `Input `parameter hover is changed into `tooltip`
* Catches more errors, improved logger information, code cleaning and refactoring.

Checkout the [documentation pages](https://erdogant.github.io/d3graph/pages/html/Core_Functionalities.html#markers) for more information about edge markers.