Store char IDs of left and right endpoints of each edge
Store char IDs of left and right endpoints of each edge

Use the custom attributes "data-l" and "data-r" so that we can later
select all the edges with a given endpoint

smpcole/asoiaf-vs-tac,smpcole/asoiaf-vs-tac,smpcole/theoriginalgot,smpcole/asoiaf-vs-tac,smpcole/theoriginalgot,smpcole/theoriginalgot,smpcole/theoriginalgot,smpcole/asoiaf-vs-tac