Cleans the notebook to be suitable for inclusion in the docs.

def clean_for_doc(nb):
    """
    Cleans the notebook to be suitable for inclusion in the docs.
    """
    new_cells = []
    for cell in nb.worksheets[0].cells:
        # Remove the pylab inline line.
        if "input" in cell and cell["input"].strip() == "%pylab inline":
            continue
        # Remove output resulting from the stream/trace method chaining.
        if "outputs" in cell:
            outputs = [_i for _i in cell["outputs"] if "text" not in _i or
                       not _i["text"].startswith("<obspy.core")]
            cell["outputs"] = outputs
        new_cells.append(cell)
    nb.worksheets[0].cells = new_cells
    return nb