[0.4.0]pywgraph-Groups have arrived!

GROUPS HAVE ARRIVED!!
In the current version, an abstraction of a mathematical group has been develop. Now you can use as weights any element of a defined group. The behaviour of the objects in the previous version is still working since not specifying a group sets the multiplication group of the real numbers, which is what it used to be. The only exception is that when trying to get the weight of an empty path the return is no more 0. Now is None, but you can set anything you want just by passing the default parameter, similar to the get method from Python's dictionaries.

What's Changed

• New-approach by @josek98 in #9
• Develop by @josek98 in #10

Full Changelog: v0.3.0...v0.4.0