[Paciente8159/uCNC PR#49] 16bit bresenham

-modified motion control to reduce number of planner blocks for motions of length 0
-modified serial library too better emulate MCU behavior
-minor changes to serial interface to improve reading
-modified all step position calculations to signed integer
-complete redesign of interpolator stepping ISR functions (fixed step loop at end of motions)
-modified serial writing/reading to improve overflow detection
-modified serial interface to read buffer without waiting for CR or LF char (more reliable since it doesn’t doesn’t depend on full string count.
-16-bit bresenham optional via config file
-fixed hidden inch report mode setting
-fixed error message on disabling soft limits command with homing disabled

There are still some issues like the lagging RUN status. This might indicate some problems with the circular buffers but it seems to produce stable enough results.