                            EDGES MENU

  The edge menu can also be invoked by pressing Alt-e.

  A position (or node) can be stored in Register 2 by clicking the 
  right mouse button over it. Register 2 can be cleared using the 
  'clear register 2' button.

  Add edge:
	Create an edge specified by its two endpoints. If there are nodes
	in the Registers, they will be proposed as endpoints for the edge.
	Shortcut: Click on one of the endpoints with the left mouse button
	then twice on the other endpoint with the right mouse button.

  Modify edge:
	Modify an edge (change its weight, outline). If there nodes in
	the registers and an edge exists between them, that edge is
	proposed for modification. If there is more than one edge between 
	the two nodes, the lastly added edge between them is modofied.

  Edge info:
	Display information about an edge, i.e., its endpoints, weight 
	and outline. If there are nodes in the registers and an edge
	between them, that edge is proposed.

  Delete edge:
	Delete an edge. If there are nodes in the registers and an edge
	between them, that edge is proposed for deletion.
