Issue in the doc with DOI of paper from VanLandingham (2001)...

[DavidMercier]

VanLandingham M.R., "Nanoindentation of Polymers: An Overview" (2001).
http://dx.doi.org/10.1002/1521-3900(200103)167:1<15::AID-MASY15>3.0.CO;2-T

in models.rst...