Add duecredit citation.

This is a low-cost way to give credit to the relevant publications. This will
only express itself, if the user runs it with duecredit. But when that happens,
we'll be ready!

shablona/due.py

@@ -0,0 +1,65 @@
+# emacs: -*- mode: python; py-indent-offset: 4; tab-width: 4; indent-tabs-mode: nil -*-
+# ex: set sts=4 ts=4 sw=4 noet:
+# ## ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
+"""
+
+Stub file for a guaranteed safe import of duecredit constructs:  if duecredit is
+not available.
+
+To use it, just place it into your project codebase to be imported, e.g. copy as
+
+    cp stub.py /path/tomodule/module/due.py
+
+Note that it might be better to avoid naming it duecredit.py to avoid shadowing
+installed duecredit.
+
+Then use in your code as
+
+    from .due import due, Doi, BibTeX
+
+
+Examples
+--------
+
+TODO
+
+
+License:
+Originally a part of the duecredit, which is distributed under BSD-2 license.
+"""
+
+__version__ = '0.0.4'
+
+class InactiveDueCreditCollector(object):
+    """Just a stub at the Collector which would not do anything"""
+    def _donothing(self, *args, **kwargs):
+        """Perform no good and no bad"""
+        pass
+
+    def dcite(self, *args, **kwargs):
+        """If I could cite I would"""
+        def nondecorating_decorator(func):
+             return func
+        return nondecorating_decorator
+
+    cite = load = add =  _donothing
+
+    def __repr__(self):
+        return self.__class__.__name__ + '()'
+
+def _donothing_func(*args, **kwargs):
+    """Perform no good and no bad"""
+    pass
+
+try:
+    from duecredit import *
+    if 'due' in locals() and not hasattr(due, 'cite'):
+        raise RuntimeError("Imported due lacks .cite. DueCredit is now disabled")
+except Exception as e:
+    if type(e).__name__ != 'ImportError':
+        import logging
+        logging.getLogger("duecredit").error(
+            "Failed to import duecredit due to %s" % str(e))
+    # Initiate due stub
+    due = InactiveDueCreditCollector()
+    BibTeX = Doi = Url = _donothing_func

shablona/shablona.py

@@ -2,10 +2,16 @@
 import pandas as pd
 import scipy.optimize as opt
 from scipy.special import erf
+from .due import due, Doi, BibTeX
 
 __all__ = ["Model", "Fit", "opt_err_func", "transform_data", "cumgauss"]
 
 
+# Use duecredit (duecredit.org) to provide a citation to relevant work to
+# be cited. This does nothing, unless the user has duecredit installted,
+# And calls this with duecredit (as in `python -m duecredit script.py`):
+due.cite(Doi("10.1167/13.9.30"))
+
 def transform_data(data):
     """
     Function that takes experimental data and gives us the