Major rewrite of serial stuff. Barely tested. Does not work.
v0258 rewritten serial_receive to speed up things and avoid congestion
v55 contains tests to debug st4 problems
R54 motions are ok.
v53 : needs to change speed directly on receiving :I when sidereal
ajout des swreqdelay non pris en compte
passage en v2 r51 a cause des mauvais numeros dans Variables.h
derniere modif prudente. Marche presque.