Wrapper for x2sys_cross

[weiji14]

Description of the desired feature

Implement x2sys_cross which "Calculate crossovers between track data files". Part of the 'x2sys` suite of modules!

Reference:

Wessel, P. (2010). Tools for analyzing intersecting tracks: The x2sys package. Computers & Geosciences, 36(3), 348–354. https://doi.org/10.1016/j.cageo.2009.05.009

Are you willing to help implement and maintain this feature? Yes