v0.11.1: Edge masking introduced

• updated readthedocs configuration file
• added new node classes MemoryNode and MemoryNet that allow to implement delay coupling in networks
• renamed the FunctionNode class into InstantNode to better set it apart from other node types that have some type of intrinsic memory
• improved method for detaching tensors via Network.detach() - provides more control over which tensors to detach now.
• debugged FeedbackNetwork.compile() method to work with multiple calls of the method
• introduced edge masking as a new feature. Can be used by passing a mask array to the keyword argument mask of Network.add_edge