old_contents: from .file_io import (ReadFITSImage, ReadFITSTable, ReadASCIITable, ReadTable, WriteTable,
                        WriteASCIITable, WriteFITSTable)
  from .stile_utils import Parser, FormatArray, fieldNames
  from .binning import BinList, BinStep, BinFunction, ExpandBinList
  from . import treecorr_utils
  from .treecorr_utils import ReadTreeCorrResultsFile
  from .data_handler import DataHandler
  from .sys_tests import (StatSysTest, CorrelationFunctionSysTest, ScatterPlotSysTest,
                          WhiskerPlotSysTest)
  
new_contents: from .file_io import (ReadFITSImage, ReadFITSTable, ReadASCIITable, ReadTable, WriteTable,
                        WriteASCIITable, WriteFITSTable)
  from .stile_utils import Parser, FormatArray, fieldNames
  from .binning import BinList, BinStep, BinFunction, ExpandBinList
  from . import treecorr_utils
  from .treecorr_utils import ReadTreeCorrResultsFile
  from .data_handler import DataHandler
  from .sys_tests import (StatSysTest, CorrelationFunctionSysTest, ScatterPlotSysTest,
                          WhiskerPlotSysTest, HistogramSysTest)
  
subject: Add HistogramSysTest to __init__.py (#17)