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

lloda 460ddcbfeb Try github workflow		1 rok temu
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FindGuile.cmake	b6da7436f9 Try Travis both on included and generated bindings	5 lat temu
UseLATEX.cmake	0112005ee3 Documentation setup	5 lat temu
protos.scm	460ddcbfeb Try github workflow	1 rok temu