Explicit specification of inter-layer reference pictures, using a layer-specific GOP structure, with 0.x syntax (0=same POC, x=reference layer).
When ExplicitILRP is true, AllowablePredDirection should not be used or left to default values (all zero), and inter-layer reference pictures are no longer inserted automatically.

This reverts commit 22c6b619.

Express frame rate as ratio of two integer values throughout code
using struct Fraction

Add support for defining fractional frame rate from command line