Add directional coefficients of friction

Currently MoorDyn-F supports friction coefficients for lines in both the axial and transverse directions while MoorDyn-C only has a general seafloor contact coefficient of friction. Adding this feature is an improvement I have chatted with @mattEhall about for the C code. 

You can see more in the [docs](https://moordyn.readthedocs.io/en/latest/inputs.html#id4).