Implement various measures of tortuosity

[jni]

Tortuosity has been defined in many different ways in the literature:

From https://www.europeanhealthjournal.com/2017/02/14/skeleton-based-cerebrovascular-quantitative-analysis/ :

In another study, Jens et al. studied abnormal extracranial ICAs and used lateral cervical displacement to determine tortuosity [16]. Studies by Grisan et al. and Shelton et al. concerning vessel tortuosity measurements used retinal blood vessels to calculate the ratio of arc length to chord length and curvature [17, 18].

The materials and methods contain various other approaches fitting b-splines. Would be nice to have those implemented in skan.

CC @marlene09

[CsatiZoltan]

Hi @jni,

I am not sure what you wish, but my software that relies on skan fits B-splines on the skeleton network. Maybe you can extract useful bits out of it.

[jni]

Thanks @CsatiZoltan!