proposed Graph API changes

[akissinger]

Two proposed changes to the API. (We can keep the old methods as aliases, but deprecate them if you like.)

1. I've recently overloaded * to compose diagrams in fomula-order. I.e. g * h means g AFTER h. I suggest keeping an operator for composing in diagram order, but changing it from from + to >>.
2. change auto_detect_inputs to auto_detect_io. I find current name confusing, because it does both.

[jvdwetering]

1. There is also a + operator for Circuits, where it does exactly what you would expect in Python: append the lists of gates to one another. So we could remove + for Graphs, but then there is an additional syntax thing you have to remember, or we could remove + for Circuits and replace it by >>, which I find slightly less natural (although it does have precedence in C++).
2. I agree that inputs is a bit confusing, but I don't really like auto_detect_io, what about auto_detect_boundaries?