support Directory Reference

Files
file	GBilinear.cpp [code]
	Bilinear interpolator class interface implementation.
file	GCsv.cpp [code]
	Comma-separated values table class implementation.
file	GDaemon.cpp [code]
	Daemon class implementation.
file	GException.cpp [code]
	Exception handler interface implementation.
file	GFilename.cpp [code]
	Filename class interface implementation.
file	GNodeArray.cpp [code]
	Node array class implementation.
file	GRan.cpp [code]
	Random number generator class implementation.
file	GTools.cpp [code]
	Gammalib tools implementation.
file	GUrl.cpp [code]
file	GUrlFile.cpp [code]
	File URL class interface implementation.
file	GUrlString.cpp [code]
	String URL class interface implementation.