Idpflex

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* cluster random distance (PR 87)
* decorator to create a namedtuple out of a dictionary (PR 86)
* drop support for python 2.x (PR 83)
* Add function fit_at_dept (PR 81)

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* Check for executable dssp (PR 79)
* Conda support to build readthedocs (PR 76)
* Check for executable crysol (PR 77)
* Added a statement-of-need (PR 73)

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* implement K-means clustering (PR 67)
* Added Asphericity property (PR 65)
* Added SASA property (PR 64)
* Added end-to-end property (PR 59)
* plot histogram for ScalarProperty (PR 56)
* Added Radius of Gyration property (PR 53)

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* Update notebook and docs with data repo (PR 51)

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* Fix secondary structure plots

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* Bug in add_property