Merge branch 'release/spectral_methods_chapter' into develop
starting CROR
starting CROR part
readding deleted files
CROR, similarity coeffs done
working on adv and lim
AEL and CROR are separated
demonstration of the thrust formulae
starting global efficiency
efficiency part
compiling to send to everyone
cror work in progress
CROR first part
starting DREAM
starting numerical stuffs
reorganization STCF11
correcting some references
starting propeller phenomena
main physical phenomena propeller, staring unsteadiness CROR
cror part corrections