improvements related to interface of tracking functions:
improve docstring of line_pass and ring_pass functions;
fill lost_element and lost_turn with -1 for particles that were not lost;
lost_flag is now a list of booleans for each particle;
change order of arguments in element_pass, line_pass and ring_pass so that they are sorted by constant inputs, changing inputs and pure outputs;
create separated method to check if particle was lost;
in python interface: fill numpy array of initial tracking coordinates with the coordinates at the point where particles were lost. For surviving particles, nans are used.
improvements related to interface of tracking functions:
line_passandring_passfunctions;lost_elementandlost_turnwith-1for particles that were not lost;lost_flagis now a list of booleans for each particle;element_pass,line_passandring_passso that they are sorted by constant inputs, changing inputs and pure outputs;nansare used.