Test on both 7.4.2 and 7.6.3
Add an embryonic RealFloat class containing atan2
Add missing RealFloat modules
Fix names of unsigned shift and rotate operators
Rewrite division as shift for unsigned numerators

Now only applies to unsigned expressions, since in C shift right is
implementation defined for signed types.
Optimize nested constant right shifts
Adapted to syntactic 1.10 with new tree drawing functions