Simplified int & float formatting routines
The default rust integer and floating point formatting routines require a huge amount of stack space, which is unsuitable for embedded programming.
Measurements I made showed that calling println! requires approx 650 bytes of stack, and calling println!("{}", 1); adds an additional 180 bytes of stack on top of that.
For floating point, it requires an additional 1.5K (over the 650 bytes of base).
These routines format into an already allocated buffer which allows for reduced heap usage.
