Improved inverse passage time function

New shc_lv_invpassagetime(). Combined default fast analytic-based solution using stoneholmesinvpassagetime() with optional quadrature and pchip interpolation methods via 'method' argument. Function now requires a Delta input, the neighborhood size. Eta renamed to Epsilon. Only SHC network structure supported.

wrightOmegaq() also updated to address issue of small imaginary errors being return for common case of x+pi*i where x<-1.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>
New function check if network is an SHC cycle

New shc_lv_iscycle(). Only supports floating-point networks, not symbolic ones.

shc_lv_isstable() help and variable names updated.

shc_lv_stability() help and variable names updated. Only supports network structures now. Cleaned up.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>