Bending rigidity and tilt modulus

[p-j-smith]

Is your feature request related to a problem? Please describe.
I would like a tool to calculate the bending rigidity of a lipid membrane.

Describe the solution you'd like
An implementation of the method developed by Doktorova et al., based on analysis of the real-space fluctuations of lipid splay and tilt.

Describe alternatives you've considered
Calculate the bending rigidity by fitting to a stress-strain relation (i.e. the methodology developed by Hossein and Deserno.

Additional context
The approach developed by Doktorova et al. requires the calculation of local membrane normals as well as lipid director vectors. These could be implemented in two separate analysis classes as they may each be useful for other analyses.