Switch to newlib

Now using newlib for debug and release variants. It makes the code
nearly twice as big (!) so no use at all changing the RAMbuild variant.
Actually commit the "Make debug variant produce hex-file"

...that was supposed to be part of the newlib switch
No need to include timer.h twice
Decouple reflow regulator from UI

Add the simple scheduler, allowing the reflow regulator to run
continuously now (even for standby). (obsoleting timer.[ch])
Verified that the 1-wire thermocouple interface works.
Some UI tweaks (some things temporary missing in bake mode because of
restructuring).
Reflow loop now runs 4 times per second, PID still needs tuning!
Oversampling of internal ADCs.
Timing macros replaced.
Read 1-wire thermocouple cold-junction temperatures.
Added gain and offset adjustments at the top of reflow.c (still
compile-time adjustment).
A faulty/absent TC will not be flagged as present
Change setpoint calculation for PID, should improve cool-down fan performance

By using the future value directly (and not the interpolated data) PID
regulator has a better chance of actually reaching the setpoint. Still
needs tuning though!
Also adds cold-junction logging for external TC IF
Rework low-level LCD code to pay attention to BUSY indication

Now cycle times are shorter but we do have to wait for some commands to
complete.
Also leave the currently selected chipselect active to minimize
glitches.
Hopefully solves freppac's display issues!
Add buzzer support

Short 100ms beep during boot and 1000ms after completed reflow.
Volume and frequency can't really be set because of the buzzer
oscillates on its own unlike ordinary piezo elements. Left in there for
compatibility with other UEoS projects.
Fix the buzzer commit

Incorrect type not corrected when importing the buzzer code
Lower idle refresh rate of display to 2 times per second

(When keys are pressed a refresh immediately happens anyway)
Expose more sensor readings and clean up bake mode UI

Now clearly indicates whether cold-junction temp sensor is detected or
not
Don't delay initial display update

Made the code look slower than it actually is
Main menu oven temp readout cosmetic fix
Enable watchdog and heartbeat LED

If scheduling stalls make sure watchdog bites and restarts the system.
Also implement heartbeat indication on red debug LED and outputs reset
reason on UART when booting.