Function zToAge( z )

Description:
Quick and dirty function for converting from redshift to time.

Warning: this makes some reasonable assumptions about the cosmology. It is only intended for approximate use. If you care about the details use one of the more specific functions here.

Parameters:
z (floating point)
redshift
Return Value (floating point):
'age' of photons from redshift z in Gyr
Signature:
double zToAge(double)