add compile-time assertion support to ospAssert.h
add a template library for decimal fixed-point numbers

Since the UI works with decimals, it gives a much better user
experience if we use decimal fixed-point rather than binary
fixed-point. The library tries to ensure proper handling of
scale factors, but also optimizes very nicely.
start tying the decimal values into the firmware
make ospDecimalValue<D> a POD type

It is important to be able to statically initialize it, so remove
all the constructors. Unfortunately, this makes literals a fair bit
more verbose.
add a shortcut for making literal decimal values
start the great switch over to fixed-point

This commit uses fixed-point throughout the Menu and Serial
modules, at the cost of making the PID loop not actually
be connected to them. Even with having added a whole bunch
of FP divisions due to fixed-to-float conversions, it still
cuts code size by ~1 kB.
fix a bug in ospDecimalValue::rescale<newDEC>()
satisfy a compiler warning
pulled fixed point code for menu/serial and fixed conflicts
fixed calibration and window menu items
MyLiquidCrystal class, input card calibration parameter