Example Python routines to help with i/o of merger trees

* README - this file

* dumptree.py - An example of how to create and populate an hdf5 file, in the
  correct format, in python

* readtree.py - An example of how to read an hdf5 file, in the correct format,
  in python

* mt.py - Utility class used by dumptree.py and readtree.py to make i/o easier

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* script_smt2hdf.py - driver script to convert Sussing Merger Tree ascii trees
  to HDF5 format

* smt2hdf.py - main routines to to convert Sussing Merger Tree ascii trees
  to HDF5 format

* tree.py - Defines a tree class and associated methods that can be used to
  iterage over spatial, temporal, or combined merger trees.

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* tracetree.ipynb tracetree.py - example of how to read in an HDF5 file and 
  do a spatial and/or temporal search.

* extracttree.ipynb extracttree.py - example of how to read in an HDF5 file
  and extract into a structured numpy array the data corresponding to one tree.

* modifyhdf5.py - example of how to read in an existing HDF5 file and modify
  the data.
