`.build()` prints to stdout. Makes capturing output difficult.

[bac]

The flowsynth build method on Model prints summary information to sys.stdout. It is awkward to actually get that output if you want to do something with it, e.g.

    # Flowsynth prints summary information directly to stdout. We must temporarily
    # redirect stdout in order to capture it.
    temp_stdout = io.StringIO()
    with contextlib.redirect_stdout(temp_stdout):
        fs_model.build()
    output = temp_stdout.getvalue()

It would be much more usable if the build method returned that data as a string. When flowsynth is called from the command-line it could simply print the results.

[whartond]

Makes sense. Do you want to submit a PR?

[bac]

Sure. It will be a breaking change, though. You ok with that?