The files in the package skeleton_analysis are copied from: https://github.com/fiji/AnalyzeSkeleton/releases/tag/v3.1.1
They are used to integrate the skeleton_analysis plugin into the SpermQ plugin. 
The plguins Skeletonize and AnalyzeSkeleton have been developed by I. Arganda-Carreras, see:
Ignacio Arganda-Carreras, Rodrigo Fernandez-Gonzalez, Arrate Munoz-Barrutia, Carlos Ortiz-De-Solorzano, 
'3D reconstruction of histological sections: Application to mammary gland tissue', Microscopy Research and Technique,
Volume 73, Issue 11, pages 1019-1029, October 2010.