Vertical line labels

[etimberg]

Adds support for labeling vertical lines. This was easier said than done. I think it might help overall if it was easier to look for a character at a given grid square (perhaps an accessor around the string?). That way this could all be done in one pass rather than 2 but I think that might be better in it's own PR.

From the test:

def test_vertical_line_labels():
    graph = graph_from_ascii("""
        A
        |
      (Vertical)
        |
        B
    """)

[coveralls]

Coverage increased (+0.6%) to 97.368% when pulling 6fe199b on vertical-line-labels into 83a1301 on master.

[greatestape]

What should this do? Error?

        A     C
        |     |
      (Vertical)
        |     |
        B     D

[greatestape]

Similar case

        A     
        |     
      (Vertical)--C
        |     
        B     

[etimberg]

I think both those cases are errors because a wire can only connect two nodes and both cases violate that

@AnjoMan thoughts?

[AnjoMan]

I agree those are both error cases. (label) is not a node