clrs graph extension: the name of Vext and Eext must be different. add macro for auto detecting if a extension is for vertex or for edge.
clrs graph extension: the name of Vext and Eext must be different.
add macro for auto detecting if a extension is for vertex or for edge.

Signed-off-by: Yi Qingliang <36380975b124e1c123f6f25e4b18a8f5e5597b95@gmail.com>

walkthetalk/clrs_chinese_solution,walkthetalk/clrs_chinese_solution,walkthetalk/clrs_chinese_solution