Added more of the SI prefixes.
made comment grouping clearer
created acceleration units type; simplified things
recreated gravity constant
added lint32_t etc typedefs for convenience
specified using lasercake_ints for world constants
added 'velocity' and 'acceleration' types, used one for gravity constant
changed some 'fine_scalar's to 'distance's
make physical_quantity not wrap its base type
Merge remote-tracking branch 'eli/unitizing1' into unitizing1
update physical_quantity<> uses for it not wrapping the num type