v0.10.1: New methods for altering Network parameters

• added a new method Network.clear() that removes all nodes and edges from a rectipy.Network instance
• added new keyword arguments to Network.detach() that allow to customize the behavior of the method with respect to which tensors are going to be detached and whether they should require a gradient after detachment or not
• added a new method Network.set_var() that allows to change the values of variables in the network instance
• added a new method Node.set_param() that allows to change the values of parameters of the node
• improved documentation of the methods of rectipy.Network