Add analysis for dimensionless overlap and interdigitation length

[blakeaw]

Add computation of the dimensionless overlap parameter and interdigitation length from

Chinmay Das, Massimo G. Noro, Peter D. Olmsted,
Simulation Studies of Stratum Corneum Lipid Mixtures,
Biophysical Journal,
Volume 97, Issue 7,
2009,
Pages 1941-1951,
ISSN 0006-3495,
https://doi.org/10.1016/j.bpj.2009.06.054.
(http://www.sciencedirect.com/science/article/pii/S000634950901279X)