lloda/prop-618: Propagation models for Earth-space communications from ITU-R P.618

lloda ac5000e231 Implement scintillation loss		5 éve
..
P1510	ac5000e231 Implement scintillation loss	5 éve
P453	ac5000e231 Implement scintillation loss	5 éve
P618	35214e7469 Progress	5 éve
P676	35214e7469 Progress	5 éve
P835	0a57159731 Include geographic atmosphere data from ITU-R P.835	5 éve
P836	ac5000e231 Implement scintillation loss	5 éve
P837	35214e7469 Progress	5 éve
P839	35214e7469 Progress	5 éve
P840	0c3f94df36 New function p840_Lred	5 éve
README.md	34dbc5c475 Release comments	5 éve

All the data in here is part of one of the relevant ITU recommendations (ITU-R P.xxx) according to the name of each directory.