dda.c: re-introduce ACCELERATION_TEMPORAL.

The implementation is slightly different this time, as it's not
using these famous bresenham algorithms. The intention is to
allow axis-independent movements, as it's required for
EMC-quality look-ahead.
Make the step timer fit for very short delays.

This isn't the magic patch which suddenly allows us to run at
arbitrary high step rates, but can deal with short bursts of
very short delays only. Typical for a 45 deg move when using
ACCELERATION_TEMPORAL.

The implementation simply extends the impossible small delay.
To keep overall timing promises regardless, the extra is stored
and compensated for when a longer delay request comes in.

Wrapped all this in #ifdef ACCELERATION_TEMPORAL, as this adds
about 300 bytes of binary size, so it likely slows down the
setTimer() code a bit and non-temporal algorithms are expected to
never request an unreasonable short delay.
Save status register on each interrupt.

Costs 28 bytes binary size and two CPU cycles per interrupt,
at the advantage of getting rid of possible well hidden bugs.
dda.c: get rid of a unused variable warning.
Teach ACCELERATION_TEMPORAL to respect maximum feedrates.
dda.c: axis_to_step = ' ' is no longer needed.

The need for this was a result of failing code in timer.c, which
was fixed in recent commits.
dda.c: initialize dda.c properly.
dda.c: remove the hack to set a minimum delay.

This in no longer needed, as the timer handles very short delays
now properly.
sersendf.c: update comment.
Stop .gitignoring configs so I can track my changes

The main repo doesn't want to know about each person's different
configurations.  But I need to track my changes over time so I can
revert back to previous releases.  So stop ignoring these config
header files in the repository.
Faster X and Y feedrates after experimentation
More feedrate tuning: x, e, x-max, y-max, acceleration
WIP: Swapped thermistor pins to match physical labels

TODO: Undo these and create new labels for my controller board.
Reduce MAX-Y and acceleration after heatbed testing

The y-axis speed worked really well and smoothly with a fast
acceleration and at high speeds (18000 steps/sec) when it was
unloaded.  But tests with the ~1100 gram heat bed attached
show that the maximum attainable speed dropped about 20%.  I
can safely get up to about 14000 now.  But I set the max to 12000
to keep a bit of safety margin.

Similar tests with the Z-axis (no loading) so I've bumped the
speed there up a bit, too.
Customize my makefile
Teach Makefile to find my ttyUSB* automagically

My serial port connection varies from ttyUSB0 to ttyUSB1 each time
I unplug/plug my USB cable in.  This means my makefile has to tweak
each time, too.  Fix this in the makefile by teaching him to assume
that the first /dev/ttyUSB[0-9] is the one I want to use.
Tune my thermistors based on measured R2 values.
Revert my thermistor pin settings to defaults
config: More steps/mm tuning

It all seems about right except extruder is about 1/3 to 1/5
the actual "needed" value.
heater: Add M203 for RepetierHost PID graphing

RepetierHost supports a streaming temperature PID graph option in the
client.  It is enabled using M203 Snnn, where the <nnn> is the heater
control to monitor (0=Extruder1, 1=Extruder2, 100=HeatedBed, 255=disabled).

See: https://github.com/repetier/Repetier-Host/wiki/Temperature-control

Add support for this feature so Teacup can be monitored by RepetierHost.

Signed-off-by: Phil Hord <hordp@cisco.com>