run-in-simulavr.sh: clean up tracein file after being done.
run-in-simulavr.sh: move statistics to the end.

This is more convenient for obvious reasons, you no longer have
to search all the output for these few lines.
dda.c: don't bit-shift c0.

While this shifting meant to increase accuracy, there's no actual
use of it, other than that this value gets shifted back and forth.
Let's start to get rid of it.

Performance stays exactly the same:

    SIZES             ATmega...  '168    '328(P)    '644(P)    '1280
    FLASH : 20188 bytes          141%       66%        32%       16%
    RAM   :  2318 bytes          227%      114%        57%       29%
    EEPROM:    32 bytes            4%        2%         2%        1%

short-moves.gcode statistics:
LED on occurences: 888.
LED on time minimum: 306 clock cycles.
LED on time maximum: 722 clock cycles.
LED on time average: 315.253 clock cycles.

smooth-curves.gcode statistics:
LED on occurences: 9124.
LED on time minimum: 311 clock cycles.
LED on time maximum: 712 clock cycles.
LED on time average: 361.416 clock cycles.

triangle-odd.gcode statistics:
LED on occurences: 1636.
LED on time minimum: 306 clock cycles.
LED on time maximum: 712 clock cycles.
LED on time average: 334.319 clock cycles.
DDA: don't bit-shift c_limit, c_limit_calc either.

Admittedly it looks like advancing in babysteps, but really
catching every bit shifting instance isn't trivial, sometimes
these shifts are already embedded in other calculations.

Still no binary size or performance change.
DDA: don't bit-shift dda->end_c either.

Next babystep. All changes in ACCELERATION_REPRAP, which isn't
part of current test procedures, so let's cross fingers it was
done right.
DDA: don't bit-shift dda->c_min.

Another babystep. First results: binary 4 bytes smaller. Yikes!
Ha ha.
DDA: don't bit-shift move_c.

Next babystep, tiny enhancement: 8 bytes less binary size.
DDA: finally, don't bit-shift dda-c.

This was the goal: not to bit-shift when calling setTimer(). Binary
size another 40 bytes off, about 1.2 % better performance:

    SIZES             ATmega...  '168    '328(P)    '644(P)    '1280
    FLASH : 20136 bytes          141%       66%        32%       16%
    RAM   :  2318 bytes          227%      114%        57%       29%
    EEPROM:    32 bytes            4%        2%         2%        1%

short-moves.gcode statistics:
LED on occurences: 888.
LED on time minimum: 302 clock cycles.
LED on time maximum: 718 clock cycles.
LED on time average: 311.258 clock cycles.

smooth-curves.gcode statistics:
LED on occurences: 9124.
LED on time minimum: 307 clock cycles.
LED on time maximum: 708 clock cycles.
LED on time average: 357.417 clock cycles.

triangle-odd.gcode statistics:
LED on occurences: 1636.
LED on time minimum: 302 clock cycles.
LED on time maximum: 708 clock cycles.
LED on time average: 330.322 clock cycles.
DDA: replace ACCELERATE_RAMP_LEN with a proper function.

This was (hopefully) the last place where this STEPS_PER_M_X-
assumption was in use.
dda_lookahead.c: get rid of a number of unused functions.

... including the last function which did the STEPS_PER_M_X
assumption.
dda_lookahead.c: note TODO on looping needs.
dda_lookahead.c: do statistics when debugging, only.

This saves a surprising 140 bytes flash and 4 bytes RAM, so
likely a nice little speed enhancement.
dda_lookahead.c: sort more statistics stuff.

Another 40 bytes flash and 8 bytes RAM off.