Investigate the potential of adding specalisations for fixed points with zero-width fractions

[Pharap]

At present there's a strong possibility that the compiler does not optimise fixed points defined with a zero-width fraction part due to the extra operations required for fractional fixed points.

Although I think it's unlikely that anyone would actually want to use a fixed point with a zero-width fraction part (because this would be more or less equivalent to an integer of the same size), I think it would be good to specialise this case at some point on the off chance that there is a genuine need for such types given that there's a clear way to optimise in this situation.

In particular, some of the possible optimisations are:

• getInteger() can avoid shifting by simply returning this->value.
• getFraction() can avoid shifting by simply returning 0.
• Multiplication and division do not need to upscale and downscale.
• roundFixed() and similar functions could simply return their argument.
  • (They would effectively become specialisations of the identity function.)