Argument for specifying input data format

[mkborregaard]

Right now Assemblage and to some degree ComMatrix accepts the input in a long range of formats, and tries to guess the format from the data. Instead the constructors should accept an "input format" argument explicitly specifying how the input data is formatted, with a beefy docstring. This should make inadvertent errors much clearer. Add a verbose kwarg with default true that specifies how the input data was interpreted.