Input validation and improvements for Neighborhood size function

Added input validation and case for non-identical nodes to shc_lv_neigborhood().

Minor bug fixes for shc_lv_invpassagetime() and stoneholmesinvpassagetime().

Signed-off-by: Andrew D. Horchler <adh9@case.edu>
Overhaul of general mean passage time function for Lotka-Volterra

shc_lv_passagetime() cleaned up to use style similar to shc_lv_invpassagetime(). Now takes Delta neighborhood size argument. D renamed to Delta internally. Eta renamed to Epsilon. Td renamed to Tt. Added optional options structure arguments to pass tolerance (not ideal as no optimization is used, but the input format matches shc_lv_invpassagetime()). Added support for Lobatto quadrature (quadl()). Changed integrand sub-function to Eq. 2.27 in Stone & Holmes 1990, which seems to yield to quadrature much better. Re-ordered some arguments to sub-functions.

Minor fixes and improvements to shc_lv_invpassagetime() and shc_lv_neighborhood().

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