$|\Delta eta|$ calculations from 3-vectors

Functions
double	Rivet::deltaEta (const Vector3 &a, const Vector3 &b, bool sign=false)
	Calculate the difference in pseudorapidity between two spatial vectors.
double	Rivet::deltaEta (const Vector3 &v, double eta2, bool sign=false)
	Calculate the difference in pseudorapidity between two spatial vectors.
double	Rivet::deltaEta (double eta1, const Vector3 &v, bool sign=false)
	Calculate the difference in pseudorapidity between two spatial vectors.

Detailed Description